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Beamer

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I have read a few threads here about throttle sync procedures and one thing that gets emphasised is not using the throttle cable to open the butterfly valves because of the possibility of a some play from one end to the other in the linkage.

The recommendation seems to be use the bar to lift all 3 or 4 values together to get them properly synced.

At first view this seems like a useful tip and a good precaution to take but is it really the most appropriate solution.

It seems to me we need to define the object of the exercise. Is the aim a perfect sync at tick-over with the throttle shut or best sync in slow running traffic or pick up and economy at low engine revs.

The point is that REAL running conditions will use the throttle cable to open the throttle valves and this is probably where it matters most. We need all cylinders to pull together as the throttle is opened. Failing to do so will reduce low end engine power and fuel economy. Any imbalance at tick-over can be adjusted using the bypass screws on the throttle bodies.

Wear in the throttle bodies and the linkage may be reasons to consider checking and resyncing the throttle valves.

Am I misreading or misinterpreting this point about slack in the linkage?

Thanks.

    

robmack

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My understanding is that the TB sync procedure with butterfly valves closed sets the correct idle speed of the engine. Adjusting the brass coloured screws varies the amount of air allowed into the cylinders through bypassing the closed butterflies, making sure it is uniform across all 3 or 4 cylinders. Idle speed is not set by adjusting the stop screw (common misconception).

Once the butterfly valves are cracked open by twisting the throttle, the amount of air introduced through the main throttle tubes overwhelms any air that may be flowing through the bypass jets.

At small, mid and full throttle openings, the synchronization of the air across all intakes is guaranteed by the adjustments that were made to the TB assembly at the factory (via the interlinkage screws with the blue paint)


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Dai

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That's how I understand it too. I've set up quite a few older Japanese fours using that method as well as my own bricks.


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indian036

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@robmack wrote:My understanding is that the TB sync procedure with butterfly valves closed sets the correct idle speed of the engine. Adjusting the brass coloured screws varies the amount of air allowed into the cylinders through bypassing the closed butterflies, making sure it is uniform across all 3 or 4 cylinders. Idle speed is not set by adjusting the stop screw (common misconception).

Once the butterfly valves are cracked open by twisting the throttle, the amount of air introduced through the main throttle tubes overwhelms any air that may be flowing through the bypass jets.

At small, mid and full throttle openings, the synchronization of the air across all intakes is guaranteed by the adjustments that were made to the TB assembly at the factory (via the interlinkage screws with the blue paint)

I think the idle speed is set by the FICU. Engine speed is one of the few data items fed back to the computer. Correct (even) bypass air adjustment means that the idle is smooth, as long as enough air is passing through for proper running.

Small throttle openings should indeed be guaranteed by the factory TB settings. 25+ years of wear and potential stuffing around by owners mean that the guarantee may no longer be valid.Mad

Bill


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1985 K100RT VIN 0028991 My original Very Happy (Historic rego)
1985 K100RT VIN 0029036 BOB the Blue Old Bike (Historic rego)
1990 K100LT VIN 0190452 Work in progress
1984 K100RT VIN 0023022 Work needing lots of progress

1986 K100RT VIN 0090542 Work needing lots and lots of progress
1993 K1100LT VIN 0183046 Work in progress
1993 K75S VIN 0213045 Newest toy, slightly non-original
    

RicK G

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The ECU cant adjust the idle speed all it does is react to what is fed to it from the sensors and adjusts the amount of fuel injected.


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Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

indian036

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@RicK G wrote:The ECU cant adjust the idle speed all it does is react to what is fed to it from the sensors and adjusts the amount of fuel injected.
I don't pretend to know all the ins and outs of the electronics, but the amount of fuel injected could easily be programmed to vary according to idle speed - a little more if the revs are low, a little less if the revs are high.
I'm extrapolating on general computer and fuel injection knowledge, but will be happy to be educated on the specifics of the K system. Compared to later systems, the feedback to the computer on the K is very limited.

Bill


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1985 K100RT VIN 0028991 My original Very Happy (Historic rego)
1985 K100RT VIN 0029036 BOB the Blue Old Bike (Historic rego)
1990 K100LT VIN 0190452 Work in progress
1984 K100RT VIN 0023022 Work needing lots of progress

1986 K100RT VIN 0090542 Work needing lots and lots of progress
1993 K1100LT VIN 0183046 Work in progress
1993 K75S VIN 0213045 Newest toy, slightly non-original
    

Beamer

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@indian036 , this is not a microcontroller system but what you say seems to be equally valid for a purely anologue electronic system.


@all, I'm not discussing the setting of the idle speed.

The question I am trying to clarify is whether the warning about NOT using the throttle cable ( twistgrip ) when syncing the TB is valid.

It seems to me that it should be done under true running conditions, ie. using the throttle cable with any play in the linkage which it may or may not have.

    

Beamer

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@robmack wrote:Adjusting the brass coloured screws varies the amount of air allowed into the cylinders through bypassing the closed butterflies, making sure it is uniform across all 3 or 4 cylinders. Idle speed is not set by adjusting the stop screw (common misconception).


Since EFI has feedback on engine revs, this could be a closed loop control system ( I do not know whether that is the case but suspect that it is ).

A lot depends upon which is the primary restriction to air flow: the four TB bypass screws or the AFM bypass.

Since the AFM bypass screw is there to adjust the idle mixture, it would seem logical that it the one which is the smallest and thus controls the airflow.

On this logic, the four TB screws are used to balance that air flow when the throttle valves are nominally closed.

The TB sync should initially be set with the bypass screws fully home. In this case, it will be necessary to slightly open the throttles to prevent stalling. It seems to me that this should be done in realistic running conditions, ie using the throttle cable.

Does anyone see a counter argument to that?

    

Holister

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These are my thoughts, so please feel free to shoot me down if you think I've got it wrong.

The FICU is an analogue system, therefore the amount of fuel is not programable. Engine speed is mostly a function of air mass. This is the only component we have direct control over. At idle speeds, air is regulated by the TB air bypass screws which balances theTBs.

Adjustment of the TB air bypass screws will not be valid unless the butterflys are fully closed as an open butterfly valve will render the effect of the bypass virtually ineffective.

The amount of air mass disregarded by the AFM is regulated by the AFM air bypass screw. This can only have one purpose in my mind and that is to set the flap to closed position and ready to open, signaling the FICU to inject more fuel the moment the butterflies are opened.

By changing the air mass at idle by adjusting the TB air bypass while maintaining a closed AFM flap with the AFM air bypass, you will be changing the fuel mix to either lean or rich. I don'tsee that as ideal. Therefore, logic tells me that once the TBs are balanced and the AFM flap is set to closed, the only way to set the operating idle speed is to adjust the throttle cable stop.

beamer: "... Which is the primary restriction to airflow..."
It has to be the TB air bypass adjustment imo

Beamer: "The TB sync should initially be set with the bypass screws fully home. In this case, it will be necessary to slightly open the throttles to prevent stalling. It seems to me that this should be done in realistic running conditions, ie using the throttle cable."
My understanding is that each TB bypass screw is wound in fully and then back out half a turn, one at a time. This should enable the engine to maintain revs without stalling. If stalling occurs then the bypass would need to be wound out a little further, but all should be initially adjusted the same before balancing.

If BMW intended the idle mixture to be adjustable the AFM flap would need to be set partly open so as to have some adjustment either way... lean or rich.

Just my thoughts
Cheers


__________________________________________________
1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

Beamer

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If BMW intended the idle mixture to be adjustable the AFM flap would need to be set partly open so as to have some adjustment either way... lean or rich.
Thanks Kapt H.

Unless you have a very tight, totally controlled system , the mixture must be adjustable. I don't see much room for 'if' here.


The FICU is an analogue system, therefore the amount of fuel is not programable.
It's an analogue computer. It is programmable in the sense of being real time controlled by a fixed program : hardware and not firmware. I'm not quite sure which way you meant this to read but there is a controlled quantity of fuel at tick-over which could be controlled by the cct. since it does have rpm input. I have not decrypted to circuit to the point where I can comment on whether it does or not.


Adjustment of the TB air bypass screws will not be valid unless the butterflys are fully closed as an open butterfly valve will render the effect of the bypass virtually ineffective.

There must be an overlap zone. Once the motor is at about 2000 rpm the throttle will be determining the air, the AFM will have moved and the mixture will be controlled by the EFI : an open loop system with mixture determined by the way the AFM was calibrated. ( see AFM thread ).

beamer: "... Which is the primary restriction to airflow..."
It has to be the TB air bypass adjustment imo

TB screws are quite small and 3 half turns on a fine thread is not much. My gut feeling is that the four TB apertures will be smaller but together they are at least comparable to the AFM bypass screw opening. I'm not sure that they can be regarded as being totally independent.

If it was the TB screws that dominate, then turning the AFM bypass would not have any effect until it was virtually fully home. This is not the case. In the mid range of it's adjustment a 1/8 or 1/4 turn will affect engine speed ( via mixture ).

It is possible that the AFM bypass adjustment opens the vane to take up what I've been calling the dead zone.ie the point with a very small vane opening where the resistor chain just starts to affect the voltage output to the FICU.

I don't say more that possible, but it's a valid suggestion.

Thanks for your comments.

    

Beamer

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This is all interesting to understand but is again getting away from my central question: show we avoid any play when syncing TBs or should we accept and explicitly adjust for its presence? The latter implies accepting a less than ideal idle sync in order to get best low down throttle response.

    

Brad-Man

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I'm gonna say I'm on the side that goes with the BMW service manual.

I'm sure the egineers know more than I do...


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indian036

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Leaving aside AFM,

Idle air is set and balanced by the TB bypass screws. At idle, TB butterflies should be closed, so 'all' air should go through the bypass channels. (TB butterflies will never be a perfect seal.)

TB butterflies need to open and travel simultaneously. This is factory set and 'shouldn't be stuffed around with'. (Paraphrasing factory info.)

30 years of reality says that wear and possible PO stuffing around may mean that the factory butterfly synchronisation may no longer be there, and needs re-setting. I've never had to do this, so wouldn't presume to say how it should be done, other than with great care.

I suspect that the factory would have had precision devices (physical movement? Air flow at butterfly angles?) to set them that we ordinary mortals don't have.

Bill


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1985 K100RT VIN 0028991 My original Very Happy (Historic rego)
1985 K100RT VIN 0029036 BOB the Blue Old Bike (Historic rego)
1990 K100LT VIN 0190452 Work in progress
1984 K100RT VIN 0023022 Work needing lots of progress

1986 K100RT VIN 0090542 Work needing lots and lots of progress
1993 K1100LT VIN 0183046 Work in progress
1993 K75S VIN 0213045 Newest toy, slightly non-original
    

Point-Seven-five

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I'm pretty sure the butterflies are synched at the factory on a flow bench where it would be a very quick and simple job.


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robmack

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  • L-Jetronic is an open-loop EFI system. It was designed long before closed loop was an itch in some engineer's groins. There is nothing in L-Jetronic to feedback combustion completeness information to the ECU to cause it to correct fueling.
  • The ECU is not an analogue computer. It has a digital computer in its heart but depends on analogue sensors.
  • The TPS informs the ECU when the TB is at idle, with fully closed butterfly valves. This causes the ECU to select a fuel map that pre-determines the injector open time at idle
  • Combustion air is drawn in from the air box to support ignition. The sync screws in each TB determine the volume of air supplied to each cylinder for such ignition. They are adjusted to ensure balance in the volume delivered to ensure a smooth idle.
  • The MAF air bypass provides just the right amount of additional air needed to ensure complete combustion (i.e. low CO2 levels)
  • Seating the TB sync screws fully will deny air for combustion and the engine will stall. They are opened to 1.5 turns as a baseline for the correct amount of air to support combustion at proper idle given the injector open time. Closing the screws will deny air and lower the idle speed; opening the screws will permit more air and increase idle.
  • Twisting the throttle will (1) move the TPS off-idle changing injector on-time because a different part of the fuel map is selected, (2) increase RPM and change spark timing, (3) introduce a need for more air which will open the MAF barndoor, overwhelming the MAF air bypass effect and (4) cause more air flow through the TB throat, overwhelming the effect of the TB sync screw air bypass


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Holister

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+1 all that except
@robmack wrote:

  • The MAF air bypass provides just the right amount of additional air needed to ensure complete combustion (i.e. low CO2 levels)

No matter what adjustment you make to the AFM air bypass, it will not affect the amount of air entering the cylinders for combustion. Adjustment here will only alter the position of the barndoor which as far as I understand, should be closed at Idle.
--------
The preset responses of the FICU (there's no logic here) needs to be referenced to a starting point ie; barndoor closed. If the barndoor is adjusted for mixture at idle, all fuel adjustments by the FICU will be biased thru the full throttle range.

I believe BMW intended for the fuel/ignition control system to be truley (factory) set-and-forget and the only way it can achieve that is by having mechanical starting (reference) points ie at idle, butterflys are closed with vacuum on all TBs equalised AND barndoor closed... but as Indian points out, wear and tear on mechanical parts means the system becomes less than ideal as it wears. The two weak points in the system are the AFM spring loaded wiper and the TB valves and linkages.


__________________________________________________
1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

Beamer_Bill

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Post deleted and will find more relevant / new thread



Last edited by Beamer_Bill on Thu Apr 21, 2016 9:01 pm; edited 1 time in total

    

Holister

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I don't think here is a good place to introduce individual issues. Copy your post text then delete this post and paste it into the relevent forum.
I think you have other issues other than air flow


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1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

RicK G

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@Beamer wrote:@indian036 , this is not a microcontroller system but what you say seems to be equally valid for a purely anologue electronic system.


@all, I'm not discussing the setting of the idle speed.

The question I am trying to clarify is whether the warning about NOT using the throttle cable ( twistgrip ) when syncing the TB is valid.

One thing that is important to know when setting the butterflys is dont use the choke lever to set the position because it pulls on the #4 body where the main throttle cable pulls between #2 and #3 body and the slack built into the adjusters sets different openings from one to the other. It can be a real trap.

It seems to me that it should be done under true running conditions, ie. using the throttle cable with any play in the linkage which it may or may not have.


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"Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats." from Mencken's 1919 Prejudices

Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

robmack

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Kaptain Holister wrote:+1 all that except

No matter what adjustment you make to the AFM air bypass, it will not affect the amount of air entering the cylinders for combustion. Adjustment here will only alter the position of the barndoor which as far as I understand, should be closed at Idle.
KH, so that I'm not misunderstanding what you've written, I'll replay it in my words. You're saying that the adjustment screw on the side of the MAF physically alters the position of the barn door - opening it more when adjusted inwards, closing it when adjusted outwards. There is a mechanical linkage to the door. Is this what you meant? (apologies ahead of time if I misinterpreted).

I believe there is a bypass tunnel that sucks air just ahead of the barn door and then routes it through the body of the MAF expelling it into the airbox from behind the barn door, effectively bypassing the barndoor. The volume and rate of air flow is adjusted with the screw.

The reason I believe this is because of this published information from Bosch:




Please take note of the description for part #5.


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Beamer

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[*]

@robmack wrote:
[*]L-Jetronic is an open-loop EFI system. It was designed long before closed loop was an itch in some engineer's groins. There is nothing in L-Jetronic to feedback combustion completeness information to the ECU to cause it to correct fueling.


[*]The ECU is not an analogue computer. It has a digital computer in its heart but depends on analogue sensors.


[*]


... etc.

Very good description except for one thing. Here from the Bosch description:


[*]


[*]My statement that it is an analogue computer is not really correct, it contains hybrid digital + analogue ICs. However, it is not a microprocessor controlled system.


PS. I have no idea what the asterisks are about , I did not type them :? Looks like the forum software is messing around recently.

    

Beamer

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Rick wrote:dont use the choke lever

Thanks Rick, that is indeed what I had falsely recalled as relating to the throttle.

    

Holister

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@robmack wrote:
KH, so that I'm not misunderstanding what you've written, I'll replay it in my words. You're saying that the adjustment screw on the side of the MAF physically alters the position of the barn door - opening it more when adjusted inwards, closing it when adjusted outwards. There is a mechanical linkage to the door. Is this what you meant? (apologies ahead of time if I misinterpreted).

Apology accepted Robert Smile . My understanding of how the AFM air bypass is constructed is the same as yours. I do not think there is a "mechanical linkage to the barndoor". I've read the Bosch literature as well.

This is fuel injection and not carburetion and I don't see the logic in being able to adjust the idle mixture when you have a control unit specifically designed to eliminate that need anyway.

How the air bypass operates in conjuction with the barndoor is a matter of physics.
The amount of air drawn into the engine is solely determined by the TB valves and their individual air bypass screws. Nothing will change that at any throttle setting. As a result, the same amount of air will pass thru the air intake system whether the AFM bypass is fully open or fully closed. As air is diverted thru the AFM bypass instead of past the barndoor, the force of air on the barndoor is reduced and it closes accordingly. As less air is allowed thru the bypass more air forces past the barndoor and it opens accordingly.
This of course changes the position of the sensor wiper and alters the output voltage to the ECU which adjusts the injection times accordingly and therefore the mix. However I don't believe altering the idle mixture was the intention of the designers as the correct amount of fuel for any condition is predetermined within the FICU.

The FICU gets the 'Idle' signal from the TPS.
I think the designers then expect that the TB valves will be closed as well as the barndoor with the wiper positioned on the 'Dead Zone' as it has been labeled by Beamer. This gives a set predetermined starting voltage for the FICU and it delivers a predetermined injection time for idle. A few things to note at this point....

  1. If the bypass is adjusted for idle mix here, the barndoor and wiper will adjust accordingly. How do you find the correct setting for this anyway unless you are looking for idle speed. I know bugger all about carburettors but I thought idle adjustment involved throttle and mixture.
  2. If the adjustment for idle mixture results in the barndoor slightly open (rich) then this will result in a slightly rich mix across the whole throttle range as you've effectively biased the wiper output towards the rich end.
  3. There will not be a complete range of adjustment for idle at the AFM anyway because at idle the barndoor will likely be closed or close to it so probably the only adjustment will be to the rich side by closing the bypass screw which opens the barndoor slightly. On the lean side, opening the bypass any more than when the barndoor is closed will have no effect on either the AFM output (barndoor can't close any more than closed) OR the air mass thru the TBs as no more air will pass thru the TBs than they allow.


I see this issue of idle mixture adjustment at the AFM as redundant. The FICU has been designed as a 'Black Box' solution for fuel management and it will work well provided starting parameters are set correctly. The starting point for the engine is running at idle. The starting point for the FICU is TB valves and AFM barndoor closed. Everything is monitored and adjusted from there. I would suggest that the AFM is a set-and-forget apartaus. There are no service/tuning requirements there. However, wear and tear on the springloaded wiper requires the AFM will need some attention and resetting as time goes on (read 25 years later). I wonder if the K100 designers thought their baby would be such a viable machine 25 or 30 years down the road.

Adjusting the idle imo needs to be done at the TB/throttle. I can't see any other way.



Last edited by Kaptain Holister on Fri Apr 22, 2016 3:19 am; edited 1 time in total (Reason for editing : small edits)


__________________________________________________
1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

K75cster

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Is it not the case that the Air bypass on the barn door is just there to allow idle air through, and to set the CO2 because that is what the countries in which BMW wanted to seel the bike wanted.
So at idle the bike gets a set amount of fuel and to match that you amend the BBS big brass screws to allow an even amount of air to each cylinder. 950 rpm idle is what the factory set up so that is what we aim for . alittle higher and the fuel air ratio would be leaner, a little lower and the fuel air ratio would be richer.Lean drop is a method put up by Tom Lentini on the American BMW site to set to CO2 its worth a read. It says that doing this setting allows the bike to be within a whisker of the actual CO2 percentage if you had a sucker up the bikes exhaust pipe to check its settings.
The throttle stop screw is I believe used to stop the butterflies from banging into the throttle bodies and chancing a misalignment if the butterflieswear or are changed somehow, then resetting them would be needed. But normally is it the case that the throttle stop screw is the best place to slip in a bit of flat bar to up the rpm if you need it for other purposed, certainly not for setting the idle air amount.
Its entirely possible that the TB's are just a tad out and one or more may very well and let in a smidge of air past the butterflies at idle, one would expect if you know the bike and its not playing up too much then that will be good enough for the bike and rider. If it becomes an issue later on then a flow bench at any hot rod shop should be able to set the butterflies after ensuring they have fixed the air issue. Then they can stick a blue dot of paint on the TB's screws. Surely the fiddly amongst us will build a flow bench and have no issue doing it for them selves. One would expect for the same reasons we all work on our bikes, we want alittle more refinement in the mechaniking.


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Beamer

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The amount of air drawn into the engine is solely determined by the TB valves and their individual air bypass screws. Nothing will change that at any throttle setting. As a result, the same amount of air will pass thru the air intake system whether the AFM bypass is fully open or fully closed. As air is diverted thru the AFM bypass instead of past the barndoor, the force of air on the barndoor is reduced and it closes accordingly. As less air is allowed thru the bypass more air forces past the barndoor and it opens accordingly.

I don't think this correct.

At a given rpm and a given setting of the TB screws, there will be depression in the inlet manifold which means there is a pressure drop across the AFM. There are two paths through that device. One is controlled by the bypass screw, the other is a reactive element with a progressive resistance against increasing air flow. ie a negative feedback.

If you screw the bypass to one extreme or the other the tickover will drop, indicating that the assertion that overall flow is not affected is incorrect.

I don't think that the vane ( hence resistor wiper ) will move off base at tickover. If it does I suspect the ECU will ignore it as long at the TPS is closed. This could be tested in situ.

This IMO is the function of the 50g pre-set load on the vane spring.



I have not seen any factory information about the dead zone. Whether this is a design feature used to fine tune in between step changes in the gear wheel tensioner settings or just a sign of wear, I can only guess. My guess is that it is a feature that allows continuous control when the device is initially calibrated and as I did with my test unit. That is only a guess though. All units which I have examined have had a small dead zone.

BTW german literature on the TB, labels the screws as Umlaufschrauben, which means bypass screws, not tick-over adjustments. I agree with you that tick-over is not adjustable ( other than that it can be adversely affected by incorrectly setting the idle mixture via the ATM bypass screw).



Last edited by Beamer on Fri Apr 22, 2016 4:23 am; edited 1 time in total

    

Beamer

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It says that doing this setting allows the bike to be within a whisker of the actual CO2 percentage if you had a sucker up the bikes exhaust pipe to check its settings.
That is how I set up mine and as reported on the AFM restoration thread, when I took it to the gas analyser the air/fuel ratio was 14.70 !! Exactly the theoretical ideal ratio.
The throttle stop screw is I believe used to stop the butterflies from banging into the throttle bodies

That is also the conclusion I have come to. It is indeed a "throttle stop" not a tick-over adjuster.

    

Beamer

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i wrote:This IMO is the function of the 50g pre-set load on the vane spring.

There is a fixed resistor between the wiper and gnd on pin5 which means that there is a fixed minimum output voltage with the vane closed. This will produce the fixed idle fuel amount.

The preload on the vane spring will ( I think ) be enough to keep it closed under these conditions. This allows the AFM bypass to produce a mixture range from too rich and too weak. This implies that it does affect net airflow into the engine.

Both sets of bypasses seem to have an effect on air flow and we can not simplify this to assume one or the other dominates and ignore the other.

The starting point for TB bypass screws of 1.5 turns ensures these are set in the right region and should only be moved a little from that position to balance between them.

    

Beamer

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From the Bosch documentation:



It is unclear what they are referring to as "idle speed control". Is this referring to the idle speed control capability of the EFI?

    

Holister

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@Beamer wrote:
Kaptain Holister wrote:The amount of air drawn into the engine is solely determined by the TB valves and their individual air bypass screws. Nothing will change that at any throttle setting. As a result, the same amount of air will pass thru the air intake system whether the AFM bypass is fully open or fully closed. As air is diverted thru the AFM bypass instead of past the barndoor, the force of air on the barndoor is reduced and it closes accordingly. As less air is allowed thru the bypass more air forces past the barndoor and it opens accordingly.

I don't think this correct.

At a given rpm and a given setting of the TB screws, there will be depression in the inlet manifold which means there is a pressure drop across the AFM. There are two paths through that device. One is controlled by the bypass screw, the other is a reactive element with a progressive resistance against increasing air flow. ie a negative feedback. Agree. That's basically what I've described.

If you screw the bypass to one extreme or the other the tickover will drop, indicating that the assertion that overall flow is not affected is incorrect. Not so. What's happening by adjusting the air bypass is you are simply diverting air into or away from the air vane; ergo... it moves correspondingly changing the fuel mix... rpm changes. At any throttle setting a finite amount of air mass passes thru the TBs and AFM in response to the vacuum created. With a set amount of air passing thru the AFM, the bypass screw determines what % is bypassed and what % is forced past the air vane. The laws of physics will apply.

I don't think that the vane ( hence resistor wiper ) will move off base at tickover. If it does I suspect the ECU will ignore it as long at the TPS is closed. This could be tested in situ. Many on this forum have either disconnected their TPS or adjusted them so that 'throttle closed' switch doesn't function. This gives a smoother transition when backing-off as the FICU would normally cut fuel with 'throttle-off' above 2k rpm giving hard deceleration. Not heard of any issues of this affecting idle. I'd be very interested to see this tested all the same.
In any case, if the spring load was strong enough to hold the vane in place against idle air flow plus any bypass adjustments, the vane may not open at the exact point the throttle is opened. I would say that is crucial.


This IMO is the function of the 50g pre-set load on the vane spring. I think the function of the 50g load is to hold the air vane closed at idle diverting air thru the bypass where it can be adjusted to fine tune the balance of the pre-loaded vane spring. In my scenario it will be important for the vane to begin to open the moment more air is introduced thru the TBs (ie throttle opens). Even brand new I think the vane springs would have had some variation in tension and would need some setting up/adjustment against a set amount of air movement.

I have not seen any factory information about the dead zone. Whether this is a design feature used to fine tune in between step changes in the gear wheel tensioner settings or just a sign of wear, I can only guess. My guess is that it is a feature that allows continuous control when the device is initially calibrated and as I did with my test unit. That is only a guess though. All units which I have examined have had a small dead zone. I think you are correct. It makes sense to have a well defined starting/base point for the wiper.

BTW german literature on the TB, labels the screws as Umlaufschrauben, which means bypass screws, not tick-over adjustments. I agree with you that tick-over is not adjustable other than that it can be affected by incorrectly setting the idle mixture via the ATM bypass screw. Cool


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1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

Beamer

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Thanks for your comments Kapt.

I wrote:I don't think that the vane ( hence resistor wiper ) will move off base at tickover. If it does I suspect the ECU will ignore it as long at the TPS is closed. This could be tested in situ.


Note that this is the oppose to the TPS hack which ensures that the the contact is never closed. I was discussing the vane moving while the TPS contact is closed.
KH wrote:
In any case, if the spring load was strong enough to hold the vane in place against idle air flow plus any bypass adjustments, the vane may not open at the exact point the throttle is opened. I would say that is crucial.

Crucial, no, optimal possibly. A tiny offset between the two would probably not be noticeable.

I'm not against what you are suggesting, just not as convinced as you seem to be. It is possible that the lean out method is letting the vane drop back to the very end of dead zone, where the AFM output just starts to move.



I don't see any evidence stated so far which allows a determination of whether this is the case. Some hands on experimentation seems to be needed. It should be possible to monitor AFM output on pin8 at the ECU pin 8 whilst varying the AFM bypass screw.

    

warmas

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Such an interesting thread deserves resurrection. My bike has L-jetronic AFM and FICU.
I have not inspected the ignition timing. Engine runs well, and has all the power I need.

After a more-than-sedate 140 miles on a new tankful of 87 octane pure gas my new-to-me 1985 K100 RT with fairing
returned approx. 38 (US) mpg, up a few percent after leaning the AFM spring one tooth, back to it's as received position. I had richened it a tooth to smooth low power engine operation, but didn't like the gas mileage.

In search of better fuel mileage, I needed to understand the mechanics and function of the AFM and fuel supply/preparation and intake systems.

With the throttle bodies at idle stop and not opened by the throttle cable, and with the AFM removed from the airbox and with the plenum open to atmosphere, engine running, rpm could be varied by only varying the opening of the "barndoor", which, apparently, by vision of the exhaust, and simultaneously, I think, varied the air-fuel mixture.

The AFM air bypass port is, I think, provided to bias the mixture across most of the entire rpm range, or at least the idle rpm range, I am not sure. The adjustment to the barndoor spring alters the position of the wiper with respect to barndoor deflection.
There is another adjustment to the wiper position to, I presume, adjust mixture at rpm points, but think it beyond my job description.

I also have a 1980 BMW R100 with only a small windshield. It routinely returns 45-50mpg hauling the same rider on the same roads in the same weather.
I think the K100 should return similar gas mileage.

It is very possible I might be wrong.
Comments and corrections, please?

    

Beamer

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Hi,

I published a very detailed investigation of the functionality of the Bosch AFM on this forum. I'm sure it will answer all of your questions ( and more you had not thought of yet ).

Basically messing with the teeth is a bad idea. If you read the article you will understand why. You will also be able to find out whether the output is still stable or not. Poor low running may be due to a worn track. The article explains the proper method to test its condition and move it to get a clean track if necessary, but it requires some careful work.

I'll see if I can find a link.

here it is:
http://www.k100-forum.com/t11055-bosch-air-flow-meter-restoration-summary

    

Two Wheels Better

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Your mileage seems a bit low. How is the compression in each zylinder? Valve clearances? Usage of oil over distance?

As an example, my '87 K100RS regularly returns 5 litres per 100 kilometres which is dead nut on 47 miles per US 4 quart gallon. I've seen it push 50+mpg and drop to 42+/- under heavy load & hard running. I regularly use 98 (RON) octane premium petrol, approximately equivalent to North America's 91 or 92 (AKI) octane premium gasolina.

Other things that could be a factor are: the exhaust is a Motad and only slightly more freer flowing, the intake is stock except for K1100 35mm throttle bodies, and ignition timing is set to BMW's recommended (PITA) method. I weigh about 90 kilos all wet and stand 175cm so am not a sail above the windscreen. The RS does have a 'taller' final drive ratio and a slightly sleeker barn door than the RT, too.



Last edited by Two Wheels Better on Fri Nov 30, 2018 4:40 pm; edited 1 time in total


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1987 K100RS, '93 Framed K11/K12 engine 'Big Block', '09 K1300GT, '07 K1200R, '04 R1150RT, '95 R100 Mystic, '77 R75/7.
Sniff...can you smell that? I think it might be bullsh*t.

    

Point-Seven-five

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Warmas, My K bikes get a pretty consistent 45mpg over a wide range of riding conditions except for my RT that usually gets 38 to 40mpg when hauling ass trying to get through Iowa and Nebraska on I-80. Pushing that huge RT fairing through the air at 85 mph uses a fair bit of gas.


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Present:
1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

warmas

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Gentlemen:
Thanks for the replies.
Beamer, I have read with great interest your research into the Bosch L-Jetronic AFM, after I had fiddled with the barndoor spring. I will read it a few more times. It really is a generous gift from you to have your research so easily available to the likes of me. It seems to run smoothly enough now. I think the track in the AFM is in good condition, I have examined it several times. The interior of the AFM appears pristine, so i doubt it functions any less than perfect.The precision of the construction of the AFM is truly impressive.

My results with the spring confirm your predictions. I have returned it to it's original position. Bike runs well and strong there.
I want the 45-50mpg others have reported. I may have to slow the bike down a bit. I think the idle speed/mixture combination tuning appears the only layman's method of simple mixture tuning. The Airhead Bing carb idle mixture affects fuel consumption well above idle, albeit inversely.
I understand the mechanics of the Jetronic idle air bypass. I have had it only barely, i.e. 1/2 turn open. I think it is reccomended it be considerably more open. The ability of the bypass to alter deflection of the barn door varies inversely with barn door deflection, thus the bypass becomes less significant the greater the airflow, which airflow is a function of throttle/rpm. Further idle bypass/rpm adjustment is in store for me.
I seem to recall reading somewhere one tooth tighter barndoor spring results in lower fuel burn at the expense of power.
Advancing the timing a bit may be in my future.
I want the best mileage I can get, not only because I am cheap, but because more range is helpful.

The valve clearances are within specs, I checked them a couple weeks ago.
Compression I have not yet checked, but I suspect it is good, engine seems to use no oil. I only have less than 1k miles on a 43k mile bike. I have a aircraft leakdown tester to use, and am familiar with aircraft cylinder compression symptoms and values.
Timing I have not checked, don't quite know how yet, suspect it is not too far advanced as engine does not ping under full throttle accelerations.

Fiddling with this machine is terribly interesting and educational, and comprehending it's peculiarities greatly simplifies maintenance. As a complete novice to this machine, it is a real adventure.

    

warmas

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A re-reading of my initial post reveals, I suspect, some errors of comprehension on my part.

Adjustment of the barndoor spring does not alter the position of the wiper with respect to the barndoor deflection.
Adjustment of the barndoor spring alters the deflection of the barndoor with respect to airflow past the barn door, thus biasing fuel flow to airflow. I think the relation of barndoor and wiper position in service is fixed. The relation may be altered on the bench.

    

Beamer

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If the carbon track is that good and the bike has such low mileage I would discount the AFM as the cause. Messing with a one tooth adjustment is a huge difference across the rev range and I find hard to see anything justifying changing that unless you are doing some serious tuning and changes to the motor.

The dead zone , wiper indexing provides a smaller offset but I would not touch what which is not broken.

Timing a far more likely this to check. Strobe light is an accurate way to do that, though BMW stupidly put the front wheel right in front of the Hall Effect pick-up, so it is pretty hard to get a clear line of sight.

Check that the paint marks are still on the butterfly value adjusting screws, If someone has messed with that is could hit fuel consumption badly.

Thanks for your kind remarks about my write-up. Having spent a good amount of time to understand the damned thing, I thought it would be best for more than one person to gain from that effort. I'm glad it was of use. These things are a bit mysterious and there is a heap of nonsense about them U-tube etc.

    

Laitch

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@warmas wrote:I want the 45-50mpg others have reported.
A used moto should get the Full Monty as soon as possible after it has been purchased.

Have you checked the throttle body manifold bushings for leaks? Is the airbox-to-crankcase ventilation tube in good condition? Is the air filter relatively clean? Are the fuel lines within the tank in good condition and tightly connected? Is the tank interior itself in good condition? How old is the fuel filter? Is the coolant temperature sensor transmitting appropriate values according to the coolant's temperature? Are the spark plugs of the correct type and their gaps to spec ? Are the tires relatively new and properly inflated? Is the clutch adjusted correctly?

If all those elements are in line, a long ride after balancing the throttle bodies should give you an accurate assessment of mileage and you'll be more likely to have achieved your 45mpg goal. As far as timing goes, if the Hall Effect Sensor notches are in alignment, I'd leave them and the AFM alone until you've done your post-tuneup shakedown and established a baseline.

The K100RT might weigh around 70lbs more than your R100 with its small screen. The RT fairing gives protection from wind, cold and rain but its drag might affect mileage more than you expect, as Point-Seven-five has indicated.


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1995 K75T 68,000 miles
    

warmas

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All:
Thanks again for your comments. They always are useful. Frequently I ask "why didn't I think of that?".
I think I have the bike in serviceable condition. Careful inspection of the throttle position switch and coolant sensor indicates correct operation.
Plugs, tires, clutch, crankcase vent, fuel tank, filter, lines, interior all are serviceable. To push an RT fairing with a tall windshield at 60mph represents significant work. A tankful with and without the fairing would compare mileages. It sure is nice at 50F, and almost as tender as a dinghy in a 25kt breeze.

The AFM vane (aka barndoor) spring has been returned to its original, rightful tooth/tension.
I concur that to lean a tooth changes the fueling too much.

My search for better fuel mileage continued.
Yesterday I experimented with changes to throttle bypass and AFM idle bypass adjustments.
Idle bypass adjustment, at nominal 1k rpm, does not appreciably alter airflow through the engine. It does alter vane deflection with respect to airflow, which deflection I have demonstrated alters rpm at fixed throttle through, presumably, mixture and timing changes. The more open the idle bypass, the more the rpm rises from idle while pressing the starter button. Pressing the starter button adds fuel. I think a more open idle bypass results in a leaner idle mixture, through the reduction in fuel rather than the addition of air. I think the idle bypass now is about 4.5 turns open.
The idle bypass function ends at some rather low airflow, and at that flow the vane deflects, for all practical purposes, as if the idle bypass were closed. I think.

With the throttle valves closed and bearing against their stop, rather than their bores, I adjusted the throttle bypasses for rpm and balance. Bike rides okay, not quite as smooth at low power as with a more closed idle bypass.
I don't know of any other simple fueling adjustments. There may not be any.

Please correct my misunderstandings.

    

Beamer

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If you can get vacuum gauges or Hg columns make sure that depression is roughly the same at different rmp. An imbalance can really knock performance and mileage.

I suggested earlier that you check the dabs of marker paint on the butterfly sync screws have not been broken. Some people are temped to mess with that and on a used bike there no easy way to redo the synchro., meaning it's probably not set up right if it has been touched.

    

brickrider2

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I wonder about the assertion that the RT fairing will hurt mileage significantly. Why would that be? A "naked" bike still has the rider in the profile as it moves through the air. Motorcycles are often thought to have a large drag due to their profile when underway. A relatively smoother profile owing to a well-designed fairing would seem to benefit higher mpg rather than harm it. That seems to be the lesson from observing the machines that aspire to speed records.
Is the RT fairing such a bad design? It certainly gives the rider good protection. Are we paying a high price for that?


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92KK 84WW Olaf

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I am of the view the RT/LT fairing is weight in town at low speeds where aerodynamics don't come into play, therefore a fuel penalty. In town and moving off from stationary you need the lowest weight possible.

At higher speeds like freeway/motorway the aerodynamics come into play and you gain either higher speed or reduced fuel consumption.

Many years back I bought a Honda CB500-4 which was a naked bike. But I acquired a full fairing for it and changed as the gearing to allow for a higher top speed which without any performance mods allowed it to raise top speed by 20% although the more obvious effect was reduced fuel consumption. Modifications came afterwards.


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1992 K100LT 0193214 Bertha Alaska Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 58,645 now 84,600 miles
1983 K100RS 0011175 Fricka 29,000 miles Damn K Pox
    

warmas

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All:
I have not touched the blue paint on the individual throttle bodies. It appears they all open and close simultaneously and at the same rate. I think they are quite finely sychronised.

My manometer is a vinyl tube with red automatic transmission fluid inside it. It cost almost nothing and is quite sensitive.
The datum is the body fixed to the throttle cable, at both idle and 3-4k rpm.
The imbalance in a pair of throttle body bypasses decreases rapidly with throttle opening.
It is not difficult to achieve a much less than a 1/4" ATF column difference at idle. This tells me the throttle body system is in good repair.

As regards weight and drag, to accelerate a change in mass follows a change in work.
Aerodynamic drag, to the best of my knowledge, varies with the square of speed.
My fairing is definitely built for comfort, rather than speed, sort of like me, anymore.
It could easily be the RT fairing creates more drag than a naked bike. It seems to me gusts bounce it around more than the bike with just a small windshield.
I would love to change the gearing and fairing on my bike to permit the top speed to rise 20% and reduce fuel consumption.
If I only knew how.

    

Beamer

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It appears they all open and close simultaneously and at the same rate. I think they are quite finely sychronised.
It's not appearances which count , it's gas flow. But if the paint markers have not been broken, we can put that to one side.



The imbalance in a pair of throttle body bypasses decreases rapidly with throttle opening.

The individual bypass screws will have little effect once the throttle valves start opening. If there is an imbalance higher up it is due to other things like leaky values. That it point of checking. Sounds like you have a mechanically sound machine. <50k for a brick, it is barely run in yet.


My manometer is a vinyl tube with red automatic transmission fluid


I would suggest investing in enough vinyl tube as you have cylinders. You want a real time comparison.

Be careful shutting down too quickly, this can suck the fluid into the motor. I know a guy who trashed a Kawa engine by sucking a load of Hg in like that. Plus he has nothing to refill with now since Hg is now a banned substance and virtually impossible to get. Plus spitting lots of hot mercury out into your garage is not a smart move. ( It's because of dickheads like that , that it is banned ).

Yes, a low density fluid will be very sensitive but I've seen 25cm of Hg, how much tramission fluid is that ?

    

Point-Seven-five

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This is my balancing rig. One bottle is connected to the cylinder with the vacuum line to the fuel pressure regulator. That becomes my "standard", and the others are synchronized, one at a time, to it. I have the screw on the "standard" throttle body set 1 1/2 turns from lightly bottomed.

The rig works by fluid flow from one bottle to the one with a higher vacuum. I adjust the throttle body idle air screw so there is no fluid level change in the bottles. I can set the balance so the level stays put for over a minute of idling with absolutely no change.

About the base setting of the "standard" throttle body, there is no specification that I can find as to how it should be set. I set mine at 1 1/2 turns because that is pretty much the universal setting for idle air screws on carburetors.

I guess, if you want to take the time, you could adjust the idle screws by doing idle speed plug readings. I do know that at 1 1/2 turns my plugs usually look a bit richer than I like, but since the bike idles nicely I can't be bothered to tweak it further.

You didn't mention how aggressively you were riding(rpm, speed). I have a total of 60,000 miles on three different bricks, and in my experience, fuel consumption on the RT/LT rises rather dramatically at speeds above 75mph. My daily commute is 55 miles at speeds between 65 and 75mph. This riding gets a very consistent 43-45 mpg. Running around town and on the local country roads at 45-55mph gets about 45-48 mpg. As mentioned, hauling ass on the interstate or very rural roads running at averages of 80+mph knocks fuel efficiency down to 38-40mpg.

Also, I have found that the panniers are a part of the bike's aerodynamics and that leaving them off causes the bike to lose 1-1 1/2 mpg. Tire pressure is important too. I would guess that almost everyone here inflates to 38psi front and 42 rear. Lower pressures will also cost a bit in gas mileage.

Have you run any injector cleaner through the fuel system? If the bike has been stored for any length of time there is probably a bit of varnish in the injectors that can feasibly keep them from shutting off fully allowing them to leak a little additional fuel into the engine. I run Chevron Techron, a half bottle to a tank of fuel for at least the first 1,000 miles when I get a bike, and then again for the first fresh tank of fuel in the Spring. It may be placebo effect, but my bikes seem to like it.


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Present:
1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Beamer

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Tyre pressure makes a surprising difference to mileage, it also has a down side. I was once with a friend in a car and he had the 'trick' of over inflating to save fuel. Whilst going through town he failed to see red light , so I quickly brought it to his attention. He stamped on the brakes and slid most of the way to the other side of the junction. Luckily there was no one coming the other way.

Hard tyres have much less contact area and thus much less friction with the road.

    

Point-Seven-five

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@Beamer wrote:Hard tyres have much less contact area and thus much less friction with the road.
Learned that the hard way last spring. Put 65 psi in the front tire of my RT to help set the bead and stop a slow leak. A quarter mile into the first ride of the season I low-sided on the the first right hand turn. Wasn't even going fast, the front end just slid out from under me.


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Present:
1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Beamer

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what is a season? You don't ride your bike all year ? Wink

    

Woodie

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For us, I'm not too far from .75, riding from December to March is entirely a bonus. Yesterday was absolute glorious motorcycle perfection - 12degrees C., sunny and not too wet. Today we've gone back down below freezing and also got some snow Sad There might be one spot in Canada, several thousand km's from where I am now, that might offer year round riding.


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52667
"Keep your stick on the ice. We're all in this together." Red Green
    

Point-Seven-five

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As Woodie says, around here temperatures go below freezing for about 4 months and we get up to 10 feet of snow each winter. Back in a younger day I rode all year, but it was on a 125cc that weighed about 180 pounds and had about 300 sheet metal screws in each tire. I don't think road ice would be very kind to something as big and heavy as a K bike.


__________________________________________________
Present:
1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

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