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1Back to top Go down    Odd K100 4v Problem on Wed Nov 30, 2016 1:45 pm

Point-Seven-five

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Been having a strange problem with my 1992 K100RS 4V that I have not seen anywhere else, so hoping the brain trust here might have some ideas.

When coming to a stop after a period of high speed running the engine has a tendency to shut down, usually when downshifting 2nd to 1st at about 10mph.  I can instantly restart by releasing the clutch and the engine will then idle and continue to run properly as if nothing happened.

Bike has been in use now for two years and about 8,000 miles since being in storage for an unknown amount of time.  Engine starts readily and idles smoothly at 950 rpm.  Power and acceleration are fine, throttle response is instantaneous and the engine runs smoothly.  TPS is set properly, temperature sender is working, plugs are good but a little black(she's using a bit of oil), the throttle bodies are balanced, the air and fuel filters have been recently replaced, and the rubber bits have all been inspected and found good. 

Bike has a non-catalytic Motronic and the original exhaust has been replaced with an earlier model K100 exhaust.  Plugs are NGK DR7EB and the bike has 115,000 miles.

Bike has been doing this for at least the past year so it is not a new problem.  All the above has been done since the problem surfaced.

Has anyone else experienced a similar problem?  I suspect the fuel pressure regulator, but it's such a pain in the a$$ to get at and they aren't cheap.  Hate to go after it if it's not the problem.  If it is, is there any chance of catastrophic failure?  If not, I can probably live with what it's doing until I get motivated enough to tear into it.


__________________________________________________
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
    

2Back to top Go down    Re: Odd K100 4v Problem on Wed Nov 30, 2016 2:29 pm

Chocolate

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Hello Point-Seven-Five!

I hade the same issue, but it shut down in any gear, not depending on the speed. My breaklight than went on, that's how I realized it's a electrical issue.

Does your break light turn on when the issue occurs???

I cleaned all contacts, even under the tank, issue still occurred.
Check/clean the kill switch, issue still occurred!
Replaced/cleaned the ignitionkey, since than it's OK.

Cheers



Last edited by Chocolate on Wed Nov 30, 2016 2:34 pm; edited 1 time in total


__________________________________________________
Only a few activities make me experience my senses in a way motorcycle riding does, it is like swimming in the nude in a river.
K75 BA/1992 ABS, K75 BA/1991 noABS, Ducati, Mobylette M1/1973
    

3Back to top Go down    Re: Odd K100 4v Problem on Wed Nov 30, 2016 2:32 pm

Point-Seven-five

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Everything on the bike works properly when it happens.  No electrical issues since I cleaned all the connectors when I first got the 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
    

4Back to top Go down    Re: Odd K100 4v Problem on Wed Nov 30, 2016 2:58 pm

Inge K.

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Check ekshaust valve clearances, if not allready done lately.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

5Back to top Go down    Re: Odd K100 4v Problem on Wed Nov 30, 2016 4:59 pm

Point-Seven-five

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Inge, exhaust valve clearance was checked last winter about 5,000 miles ago and were shimmed to be at the top of the spec(with max clearance).

Problem predates clearance check and the maintenance work done last winter. 

Is it possible that the fuel pressure regulator is taking the pressure on the rail too low to maintain proper fuel injection?  I know the vacuum line to the throttle bodies is supposed to do something to regulate the pressure under different engine loads, but I am not that knowledgeable on how the regulator works.


__________________________________________________
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
    

6Back to top Go down    Re: Odd K100 4v Problem on Wed Nov 30, 2016 5:59 pm

indian036

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@Point-Seven-five wrote:Is it possible that the fuel pressure regulator is taking the pressure on the rail too low to maintain proper fuel injection?  I know the vacuum line to the throttle bodies is supposed to do something to regulate the pressure under different engine loads, but I am not that knowledgeable on how the regulator works.

I don't have any ideas for the specific problem, but the operation of the Fuel Pressure Regulator is pretty straightforward in principle.

By internal spring pressure, it maintains a constant pressure (36psi?) in the injector rail. It does this by releasing 'excess' fuel back to the tank via the return line.
The vacuum line adjusts the spring pressure via a diaphragm to increase the fuel pressure slightly when under acceleration (throttle opened wider = lower intake vacuum). This means that under acceleration, more fuel is injected because of the higher fuel rail pressure. The injector opening duration remains as specified by the fuel computer in the circumstances at the time. Under steady throttle and deceleration, the vacuum connection has no significant effect.

Short of replacing the FPR, if you can put a fuel pressure gauge in the pressure side of the fuel system (anywhere between the tank and the FPR) with a long enough hose to attach it to a position that's visible when riding, at least you'll be able to see what happens to fuel pressure in those circumstances. Make sure connections and attachments are secure. Fuel spraying around is not nice. Very Happy  They are usually attached via a T piece somewhere in the line.

Bill


__________________________________________________
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
    

7Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 2:19 am

K75cster

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Does it occur if you whilst riding along at speed simply clutch in and heavy braking.
Should it occur by weight transfer, then perhaps the key or the four prong power feed to the tank may be suspect, or perhaps a wire exposed in or around the head stem, just coming into contact with the heavier braking.
Or maybe do you actually brake heavier in the upper gears than in just the 2nd to 1st issue, cause I cant see a connection from 2nd to 1st in the sender to the binnacle or anything like that.


__________________________________________________
Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

8Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 4:32 am

Holister

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Point-Seven-Five, I had the exact same problem back in 2014 with my 89K100. Had me and others baffled for months.
The original problem
http://www.k100-forum.com/t8442-engine-cutout-on-throttle-off
And the resolution
http://www.k100-forum.com/t8442p100-engine-cutout-on-throttle-off#110317
The short story.... exhaust valve clearances were way too tight on the front three pots.
The end result is that I think the valves weren't closing and there's a possibility that they are now burnt. The old girl has now been retired for the best part of this year and is in storage till I can get to her sometime next year. Just been a really busy year for me.

If you've done the shims, maybe best to check the compression to make sure there's no valve damage. Damage may have been done prior to your ownership. Once burnt they only get worse.

Hope this helps
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
    

9Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 12:13 pm

Point-Seven-five

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Lots of good comments and information so far.  It's good to know how the FPR works.

As far as exhaust valve gaps, they were still in spec when I checked them last winter.  I only reshimmed two of them to open the gap to maximum and make them all nearly equal.  When I had the head off to replace the valve guide seals I inspected the valves and all were good with no sign of burning or excessive seat wear.  Compression was checked prior to removal and it was found to be good and balanced between all cylinders.

To describe the problem a little better, imagine coming down the off ramp of an expressway where you have been riding at 60+ mph for the past 10 or more miles.  You slow down through use of the brakes and engine braking until you get to where you are about 10 feet from the point where you want to come to a complete stop.  You pull in the clutch and apply the brakes and the engine quits.  You are still rolling at a couple mph so you pop the clutch and the engine starts, you pull the clutch and brake to a stop with the engine idling perfectly.

This only occurs after high speed riding.  I can ride in city traffic at low speeds all day and never have the engine stall like this.

Besides the FPR i am suspecting the possibility of a momentary oil fouling of the spark plugs.  I say this because the engine does use a fair bit of oil compared to my K75's, about a quart every 800-900 miles.  Several seconds of high cylinder vacuum during engine braking may be sucking enough oil past the rings to foul the plugs to the point where they momentarily stop firing.  I know it sounds like I'm grasping at straws, but I'm having a hard time thinking of any other cause.


__________________________________________________
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
    

10Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 12:24 pm

Ringfad

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I have been working through starting problems on my K1 and was also suspecting the FPR

http://www.k100-forum.com/t11883-k1-16v-not-starting

Prior to this starting issue I was seeing exactly the same problem you described in your previous post.

I have the bike apart and will be checking the FPR and Water temperature sensor soon.

I am wondering if what you (and I) have seen, with the stalling problem, is a symptom of something failing.


__________________________________________________


   ;BMW; K100RS Style Black 1987 105K Km     ;BMW; K1 Black 1993 51K Km     ;BMW; K1100RS Red 1993 70k miles  ;BMW; K100 16V Black (ex ElectricMonk)
    

11Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 12:32 pm

Point-Seven-five

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Ringfad, let me know what you find with the FPR.  Maybe I should be looking for a new one.  Is there a test that can be done to confirm it is good or bad?

As I mentioned in an earlier post, the plugs are a bit blacker than ideal, and coupled with the oil consumption I have been thinking seriously about going to a hotter plug to do a better job of burning the crap off the electrode. 

Does anyone have any thoughts on that approach?  Might do a plug change today, but the approaching snow precludes a test ride in the near future.


__________________________________________________
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
    

12Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 1:12 pm

Ringfad

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I have purchased a fuel pressure gauge and will try and figure out what is going on.

Unfortunately the location of the FPR is difficult or I would take one off one of my other bikes.

I forgot to mention I am also seeing high oil consumption.

Will keep you informed of progress but freezing here as well so not inclined to go outside at the moment. Blizzard


__________________________________________________


   ;BMW; K100RS Style Black 1987 105K Km     ;BMW; K1 Black 1993 51K Km     ;BMW; K1100RS Red 1993 70k miles  ;BMW; K100 16V Black (ex ElectricMonk)
    

13Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 1:20 pm

sidecar paul

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Here's a picture of the inside of a dead FPR.   affraid The ball of the valve is supposed to be captive behind that metal surround but wear caused it to pop out.



Paul.


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'84 K100RS (0014643) (owned since '85), 86 K100RS (0018891) with Martello sidecar (built as an outfit in '88),
'51 Vincent (since '67),'72 Montesa Cota (from new), '87 Honda RS125R NF4 (bought 2015) 
....No CARS never ever!
    

14Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 2:12 pm

Point-Seven-five

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Ok, it appears to me that the vacuum line to the FPR puts a negative pressure on the diaphragm of the FPR when the engine is under no load to lower the pressure in the fuel rail and thus reduces the delivery of fuel through the injectors when engine braking.

There are several reasons I can think of that make this desirable:  First, it reduces the amount of emissions during engine braking.   Second, it reduces fuel consumption.  Third, it helps to reduce backfiring.  The problem comes in when once the engine braking halts, the fuel pressure can't recover fast enough to supply the fuel necessary to prevent stalling.

Without the vacuum connection, the regulator will maintain the fuel pressure at setpoint at all times, preventing the benefits listed above.  Other than this there is no negative effect of disconnecting the vacuum line beyond backfiring, increased fuel consumption and emissions. 

A test might be to disconnect the vacuum line and plug the vacuum outlet on the throttle body and see if the problem continues.   This is what I think I will do as soon as the snow stops and the weather clears.  If the problem continues, it probably means the cause is the momentary lag in fuel pressure recovery.

I can think of several causes for this, failing FPR, restrictive fuel filter, or a weak fuel pump.  If the engine runs properly otherwise, I would suspect that the FPR is working properly.  This leaves the filter and pump.


__________________________________________________
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
    

15Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 4:33 pm

indian036

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While I can't claim to know the specific situation on a BMW K FPR, using vacuum to reduce fuel flow on deceleration would be a pretty unusual scenario. Usually, its only for more fuel on acceleration, and does nothing on steady speed or deceleration. 
The Throttle Position Switch is the component that cuts fuel when the throttle is brought back to idle level while slowing down, by letting the fuel computer know that, and the computer then switches off the injectors until the engine revs are less than a certain figure which the experts will know better than me.

Bill


__________________________________________________
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
    

16Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 7:27 pm

K75cster

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I believe that's just the 2 valve models Bill.
4 valves don't have this feature. I was wondering about having the fast idle cam on 1st or 2nd step to see if it still did it. But point 75 has put it to bed till the snow clears.

I understand the fpr is different to the early models and also I don't know If it can pick up crud from an oil using engine. Does it get sucked into the fpr for instance.


__________________________________________________
Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

17Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 7:38 pm

RicK G

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Gee I thought that the injectors cut out after about 1.5 seconds after no throttle above 2000rpm so the change of vacuum would do nothing but maybe I am wrong again.


__________________________________________________
"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
    

18Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 8:23 pm

Point-Seven-five

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According to the Bosch Jetronic manual,

http://bowlsby.net/914/Classic/zTN_Man15.pdf

the purpose of the vacuum line is to adjust the regulated pressure in the fuel rail to a set value relative to the air pressure in the intake manifold. 

Because of the vacuum line a gauge reading pressure in the rail will see it varying slightly with throttle setting and engine speed.  At high vacuum such as occurs with heavy engine braking the fuel rail pressure is reduced and as the vacuum is reduced the fuel pressure needs to increase to maintain proper pressure differential across the injectors to keep the mixture from getting too lean to fire. 

This reinforces what I think is happening.  Now all I need to find out is why the pressure is not recovering fast enough to prevent a stall.  Is it the pump, the filter or the regulator. 

Tomorrow, I will replace the fuel filter with a new one.  Might be a while to do a test ride with cold and snow in the forecast.


__________________________________________________
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
    

19Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 10:53 pm

Holister

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@indian036 wrote:While I can't claim to know the specific situation on a BMW K FPR, using vacuum to reduce fuel flow on deceleration would be a pretty unusual scenario. Usually, its only for more fuel on acceleration, and does nothing on steady speed or deceleration. 
The Throttle Position Switch is the component that cuts fuel when the throttle is brought back to idle level while slowing down, by letting the fuel computer know that, and the computer then switches off the injectors until the engine revs are less than a certain figure which the experts will know better than me.

Bill
I'm with Bill on this re FPR.

@Point-Seven-Five wrote:....
Because of the vacuum line a gauge reading pressure in the rail will see it varying slightly with throttle setting and engine speed.  At high vacuum such as occurs with heavy engine braking the fuel rail pressure is reduced and as the vacuum is reduced the fuel pressure needs to increase to maintain proper pressure differential across the injectors to keep the mixture from getting too lean to fire.
....
"Heavy engine braking" will not create a vacuum (neg pressure). If its anything it would be positive pressure.
A vacuum develops in the intake manifold under acceleration (edit: and deceleration). This creates a greater pressure differential across the injectors from the fuel rail to the intake manifold, than the FICU is expecting and has the effect of increasing fuel flow which is unmetered by the FICU. How this is corrected is by running the vacuum line to the FPR. The neg pressure then adjusts the FPR to decrease the fuel pressure to the rail thereby regulating the pressure to give an even flow between acceleration and normal running. Without the vacuum line, under acceleration, the engine will be running rich. Aside from poorer performance, the problem with this is that the FICU can only meter the correct amount of fuel by switching the injectors when pressure between fuel rail and intake are evened. There is nothing that tells the FICU what the intake pressure is as the engine status varies. The vacuum line/FPR adjusts the pressure at the rail to match the pressure/vacuum in the intake manifold so you'll always see the fuel pressure guage moving as demands change and manifold pressure varies.



Last edited by Holister on Sat Dec 03, 2016 12:52 am; edited 1 time in total


__________________________________________________
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
    

20Back to top Go down    Re: Odd K100 4v Problem on Thu Dec 01, 2016 11:08 pm

Point-Seven-five

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Did you ever operate a vehicle with a vacuum gauge?


__________________________________________________
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
    

21Back to top Go down    Re: Odd K100 4v Problem on Fri Dec 02, 2016 1:47 am

RicK G

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Over-ride engine braking does decrease manifold absolute pressure (vacuum increase) just as opening the throttle will decrease manifold absolute pressure.


__________________________________________________
"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
    

22Back to top Go down    Re: Odd K100 4v Problem on Sat Dec 03, 2016 12:56 am

Holister

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Yep.. ok. I can see I got that wrong. My bad. Embarassed I've edited my post. Manifold vacuum is produced on deceleration. So just disregard my spew of thoughts back there as its not relevant anyway. Rolling Eyes
A combination of that and not really understanding what you were getting at in your post Point75. You could be onto something with that.

One way to check your theory would be to disconnect the vacuum line and cap it off on the TB. That way there won't be any adjustment to the fuel pressure by the FPR.

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
    

23Back to top Go down    Re: Odd K100 4v Problem on Sat Dec 03, 2016 12:27 pm

Point-Seven-five

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@Holister wrote:Yep.. ok. I can see I got that wrong. My bad. Embarassed I've edited my post. Manifold vacuum is produced on deceleration. So just disregard my spew of thoughts back there as its not relevant anyway. Rolling Eyes
A combination of that and not really understanding what you were getting at in your post Point75. You could be onto something with that.

One way to check your theory would be to disconnect the vacuum line and cap it off on the TB. That way there won't be any adjustment to the fuel pressure by the FPR.

Cheers
Good idea blocking the vacuum line.  Will be getting a new fuel filter today.  Now I just need a break in the weather to get out for a test ride.  With the snow and cold being forecast, that may be a while off.  Regardless, I will report the results when I can.


__________________________________________________
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
    

24Back to top Go down    Re: Odd K100 4v Problem on Sat Dec 03, 2016 12:55 pm

Laitch

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@Point-Seven-five wrote: With the snow and cold being forecast, that may be a while off.  Regardless, I will report the results when I can.
The road are nice over here right now for test riding, Point-Seven-five. Two inches of wet snow trimmed with slush and mud. Makes for a soft bike landing when things go bad.  Smile


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1995 K75T 68,000 miles
    

25Back to top Go down    Re: Odd K100 4v Problem on Sat Dec 03, 2016 2:41 pm

Point-Seven-five

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In those conditions the need for a soft landing is almost inevitable. 

I am holding off mainly for cosmetic reasons.  Just did a complete end of season service of all fluids and splines, rear seal and o-ring replacement tune up and detailing.  Not real eager to muck everything with salt and grit.

Yeah, I'm pretty anal about my bricks.


__________________________________________________
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
    

26Back to top Go down    Re: Odd K100 4v Problem on Sat Dec 03, 2016 3:31 pm

Motorbike Mike

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@Point-Seven-five wrote:Yeah, I'm pretty anal about my bricks.
Me too.
I bought a Garage Find K1100 that had been in there since 1998. Now I've cleaned it up I can't use it in all weathers. Rolling Eyes

    

27Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 12:49 pm

Point-Seven-five

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Got her out for a ride this morning with the vacuum line disconnected from the throttle body and the vacuum port capped. 

Problem persists. 

Hard engine braking while downshifting through the gears will stall the engine when the clutch is pulled in just prior to stopping. 

Hitting the starter restarts the engine immediately.

There are absolutely no other drive-ability or performance issues with this engine.  It idles smoothly, accelerates enthusiastically with no hesitation, pulls strongly right up to 90mph where law enforcement concerns cause the rider to let off the throttle, runs smooth at cruising speed, and decelerates without backfiring.

Idle speed may be a bit low at approximately 900rpm, but otherwise I am totally stumped...


__________________________________________________
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
    

28Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 6:37 pm

Holister

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My similar problem had exhaust popping and occasionally a very loud cracking backfire as the issue got worse. So you can probably rule out valves and it looks like the FPR is now ruled out also. With all your service parts replaced and sensors checked, it looks like you are narrowing it down.

It could be that the FICU is not resuming fuel when revs fall below the 2000rpm mark as it should with throttle closed. It wouldn't be an earthing or connection issue as the fault seems very consistent. Sounds electronic.


__________________________________________________
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
    

29Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 7:01 pm

Laitch

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What do suppose would happen if you raised the idle 50 rpm?


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1995 K75T 68,000 miles
    

30Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 7:13 pm

Point-Seven-five

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Yeah, Laitch, the idle does look a little low in spite of how smooth it is.  I  am wondering how to properly raise the idle speed with the motronic system.  Do I adjust the throttle stop screw, or do I crank out the throttle body air screws?  Will I need to readjust the throttle position sensor?

Need to do some research on this.


__________________________________________________
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
    

31Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 7:49 pm

Laitch

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@Point-Seven-five wrote:Do I adjust the throttle stop screw, or do I crank out the throttle body air screws?  Will I need to readjust the throttle position sensor?
The '88 RS manual instructs using the air screws. I'd check the throttle position sensor afterward, too, since that's simple enough. Your idle is right in the center of the 950 ±50 rpm spec range.

This adjustment seems a more benign preoccupation than contemplating buying another FI control unit.  Laughing


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32Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 8:50 pm

Holister

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I don't think the low idle would cause the engine to stall when coming off throttle. The operating spec is 900 to 1000rpm so it should operate ok around the bottom of the range. It may be exacerbating the problem and if raising the idle does eliminate the stalling I think it will only be masking the symptoms to some other issue.
Still, it would be interesting to see what happens with idle set correctly at 950. Should give you some more clues as to what's happening.
Just my thoughts. Cheers


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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
    

33Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 9:30 pm

Laitch

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@Holister wrote:Still, it would be interesting to see what happens with idle set correctly at 950. 
According to the first post it already is set to 950 rpm. I was bidding for another 50 rpm. If it quits stalling by masking other symptoms, I'd consider that a win. Denial is one of my coping strategies. Smile


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34Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 10:15 pm

Point-Seven-five

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Today it looked more like 900.  There were two good needle widths of space between the 1000rpm mark and the tach needle when the engine was at operating temperature after a 15 mile run.

Have spent the evening trying to find out how to properly set the idle rpm without giving a large wad of cash to a dealer.  All I have done is start to wonder if I have a whack CO potentiometer.   It is the one thing I have not been able to check since the procedures I read all call for a exhaust gas analyzer.  The only guys around here who have them are dyno shops and they want $100/hour to check the CO.


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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
    

35Back to top Go down    Re: Odd K100 4v Problem on Sun Dec 04, 2016 10:33 pm

Holister

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@Laitch wrote: Denial is one of my coping strategies. Smile
Yes, I used that strategy many many years ago when I traveled across Australia in an old Wolseley.... OK, everybody can stop laughing now! I was young What a Face ..... the radio gradually got louder and louder so I couldn't hear the engine which eventually turned to jello as I was approaching Adelaide. Laughing

In Point75's post #27 he says.... "Idle speed may be a bit low at approximately 900rpm, ...."
The OP rpm of 950 I think is at startup. Enrichment can make it run a tiny bit quicker then. I find my old naked k100 settles down about 300 or 400rpm once she's warmed up.


__________________________________________________
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
    

36Back to top Go down    Re: Odd K100 4v Problem on Mon Dec 05, 2016 8:40 am

Laitch

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@Holister wrote:
Yes, I used that strategy many many years ago when I traveled across Australia in an old Wolseley.... I was young What a Face ..... the radio gradually got louder and louder so I couldn't hear the engine which eventually turned to jello as I was approaching Adelaide. Laughing
One of the drawbacks of living in the States is that there aren't enough Wolseleys for everybody who wants one. Laughing  In my youth, I had to settle for a '59 English Ford Escort station wagon with a flathead four and magneto crankstart option—usually deployed at a drive-in restaurant when the largest possible audience was available to be awed by my manly starting technique. Of course, the finish might have been more impressive if I'd been climbing into a sparkling Wolseley afterwards, but that was not to be.Sad

Returning to your youthful travels, Hollister, who would want to listen to an engine as it turns to jello? Your strategy was on point.
 cheers 

Point-Seven-Five's circumstance raises the question of whether we want to use logic based on sound understanding of the operational theory of this bike, or, instead, follow some crack-brained course of action based on intuition and divination. I propose the second alternative.

If the idle is increased a hair—50rpm qualifies as a hair, but perhaps that hair could be split—then the mechanical linkage or assembly clearance changes caused by hot running with an aged system that may be at the root of this condition could possibly be compensated by that increase without significantly changing overall performance. If that works, maybe later the problem's actual mechanical source can be found, if riding a bike that is idling correctly in all conditions just does not provide the necessary level of satisfaction.

The simplest approach would be to mark the position of the throttle stop screw, move it to get the increase; however, the weather this time of year in our neck of the woods isn't the best for proving engine performance. It is a great time of year for combining rum with sugar, hot water, and cinnamon then drinking the result. Regardless, if the engine's adjustment when finally tested isn't satisfactory, the screw can be returned to its original position and the t-bodies could be balanced to raise the idle. To follow The Book, it seems to me all .75 needs is a manometer to adjust the idle—like a Carbtune or a Goldbergian fabrication of tubes and two-by-fours.

The affects of skewed CO values on performance are beyond my powers of divination which are currently occupied with Lotto numbers.


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37Back to top Go down    Re: Odd K100 4v Problem on Mon Dec 05, 2016 3:49 pm

Point-Seven-five

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Well, my wrench time today is being occupied with the replacement of radiator hoses on my cage in preparation for the white stuff that is soon to blanket the landscape.  Three hours in and one of them is replaced and the other is almost out.  *%#$@ Modern cars...

Later this week I might make an attempt to adjust the idle by means of the throttle body air bypass screws.  Also need to see what the F is going on with my CO potentiometer as that may have some bearing on idle mixture and hence could feasibly have some effect on the problem.   No idea of when I'll get another chance to do a road test, but I want to be ready with the bike set up for 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
    

38Back to top Go down    Re: Odd K100 4v Problem on Mon Dec 05, 2016 4:03 pm

Point-Seven-five

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BTW, what is the basic setting for throttle body air bypass screws???

I was using 1 1/2 turns out.  Should it be more or less?  I can't recall seeing a spec for this setting's start point.  My balance rig doesn't indicate vacuum, just the vacuum balance between two throttle bodies.  My procedure is to set the #4 at 1 1/2 turns and then balance the others to it.  Works fine on my K75's.

Can anyone point me to a way to set the CO potentiometer without a CO meter?


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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
    

39Back to top Go down    Re: Odd K100 4v Problem on Wed Dec 07, 2016 1:04 am

K75cster

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My understanding is to wind them all out evenly at or about the 1-1/2 mark and then when all set evenly by the manometer wind them all evenly in by 1/4 of a turn.
Then do a lean drop test with the other side of the bike on the fam unit.

The Lean Drop method is what its called, just google it up the top of the page.


Actually the google bit is on the forum front page but I was close.
Here is one post about it  http://www.k100-forum.com/t4063-help-me-remember-a-k100-test


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Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

40Back to top Go down    Re: Odd K100 4v Problem on Wed Dec 07, 2016 1:52 am

Point-Seven-five

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It sounds like I have the throttle body air screws set properly at 1 1/2 turns out.  I don't understand the 1/4 turn in after they're balanced.  Won't that just unbalance things and lower the idle speed? 

The link you posted is for a Jetronic.  I have a non-catalytic Motronic on my 1992 K100.  It has  a CO potentiometer in place of the O2 sensor in the exhaust.  I have found some information on how this thing works and will see if I can do a lean drop adjustment with it.  BTW, I've been around so long I can remember when it was called lean best idle. 

Looks like I need to pull the tank and some of the fairing.  Maybe Thursday or Friday.  The colder it gets out in the garage, the harder it is to get motivated.


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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
    

41Back to top Go down    Re: Odd K100 4v Problem on Wed Dec 07, 2016 2:35 am

K75cster

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Bugger I got that bit wrong. must be something in here for 4valve mototronics


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Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

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