Cylinder balance at idle

Puccini · 1 Cylinder balance at idle on Thu Mar 02, 2017 10:59 am

Puccini

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Number of posts : 89

Every post I've read says that it doesn't matter where the 4 Idle balance screws are set as long as they are set the same.

For some reason that doesn't make sense to me. They regulate air flow at idle.

Is it better to balance them further closed than open?

Point-Seven-five · 2 Re: Cylinder balance at idle on Thu Mar 02, 2017 11:22 am

Point-Seven-five

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Number of posts : 2502

I have yet to find any information on this subject despite looking for it. It appears that the correct setting is derived some other way than counting the number of turns out from bottom or setting to a specific vacuum value.

I have set throttle bypass screws at anything from 1 1/2 to as many as 5 turns from bottom, and the effect on idle has been minimal. It appears that on the Jetronic systems that the bypass on the MAF has more influence than the throttle body screws. The leads me to believe that a good portion, probably most, of the idle air flow is past the throttle body buttterflies, and the idle adjust screws just act as fine tuning trim adjustment for balance.

It would be great to have someone who has been trained by BMW to chime in on this subject. The factory service manuals call out the use of a BMW special tool for idle mixture adjustment and throttle balance. That tool appears to be some sort of a vacuum device that is calibrated for some setpoint that may or may not be specified in units.

My guess is that BMW does not publish the vacuum specification in order to force owners to have idle and vacuum balance done by the dealer. They would not be the first OEM to follow that strategy.

Puccini · 3 ??? on Thu Mar 02, 2017 11:44 am

Puccini

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Number of posts : 89

Sorry, what is MAF??

Point-Seven-five · 4 Re: Cylinder balance at idle on Thu Mar 02, 2017 12:08 pm

Point-Seven-five

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Number of posts : 2502

Mass Air Flow sensor.

It's in the air box above the filter and tells the engine controller how much air and, by inference, oxygen is coming into the engine for combustion.

Puccini · 5 Re: Cylinder balance at idle on Thu Mar 02, 2017 12:25 pm

Puccini

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Number of posts : 89

@Point-Seven-five wrote:Mass Air Flow sensor.

It's in the air box above the filter and tells the engine controller how much air and, by inference, oxygen is coming into the engine for combustion.

How reliable are they? I've got an 85 K100RT that idles and runs good for the most part but it has a unsettling habit of (every now and again) sputtering and stalling when your accelerating off of idle.
And very rarely at speed I'll get a short buck out of the engine

Usually in 1st gear. I did plugs, injector cleaning, wires, fuel filter. I understand the fuel pump was replaced just before I got it. Speedo shows 28K miles and I suspect it doesn't have more than 35K on it.
Cleaned the ignition switch, kill switch is ok.
Tried unhooking the TPS and no change.
replaced the fuel lines.
I thought it was vapor lock but it idles great even when it's really hot.
No indication of an electrical failure when it happens. All gauges stay on , no indicator lights,

I cleaned the tank bottom plug for the fuel pump so I think thats ok also.

I am installing the fuel line heat insulation wrap just to cover that base. But I am annoyed with this problem and want to fix it. Any Ideas?

Point-Seven-five · 6 Re: Cylinder balance at idle on Thu Mar 02, 2017 12:48 pm

Point-Seven-five

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Number of posts : 2502

Stumbling off idle does sound to me like a lean mixture/starving for fuel. That could be a MAF sensor problem with a sticky flapper or a dirty track in the sensor where the signal is generated.

If the track or wiper is bad it is possible that vibration could momentarily create electrical noise that could cause an engine miss at speed.

I have not had any experience troubleshooting these sensors, but a search of the forum should bring up several threads by people who have more experience than I. I know I have seen threads that get into these devices in great detail.

Puccini · 7 Re: Cylinder balance at idle on Thu Mar 02, 2017 1:56 pm

Puccini

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Number of posts : 89

Thanks you could be right. Is the MAF serviceable?
I mean can it be opened and cleaned?

I'm planning on going over everything in the fuel system once it gets warmer.

Thanks
Gerry

Dai · 8 Re: Cylinder balance at idle on Thu Mar 02, 2017 2:58 pm

Dai

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Number of posts : 3920

Yes. Two bolts hold it in to the black plastic box and four (?) screws hold the aluminium box together. Be very careful - there's a thermistor in the intake and it's too easy to damage it.

RicK G · 9 Re: Cylinder balance at idle on Thu Mar 02, 2017 7:22 pm

RicK G

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Number of posts : 12303

If the throttle bypass screws are set correctly and the bypass in the MAF then you will get minimal change screwing the throttle bypass out but it will change things if they are screwed in.

Puccini · 10 Re: Cylinder balance at idle on Thu Mar 02, 2017 9:12 pm

Puccini

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Number of posts : 89

@RicK G wrote:If the throttle bypass screws are set correctly and the bypass in the MAF then you will get minimal change screwing the throttle bypass out but it will change things if they are screwed in.

You totally lost me.

I don't understand what your trying to say.
Can you expand on it?

Bekman · 11 Re: Cylinder balance at idle on Thu Mar 02, 2017 10:18 pm

Bekman

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Number of posts : 69

I'm in exactly the same boat you are with my bike and it's very frustrating.when chasing down the problem I found I had low compression of 100 psi per cyl and was able to find a good used engine for a good price. It was cheaper for an engine than to get the head done etc. when i first started it, it ran great. Then it reverted to its old self which made me chase manifold leaks etc. had fun with those Oekiter clips, bought the wrong throttle cable, but was smart enough to buy the proper hose clamps on McMaster Carr as a backup. Basically lit $100 on fire. But who are we kidding. We love spending money on motorcycles. I adjusted with vacuum gauges the throttle linkage screws. I was able to get 1,2 & 3 cylinder to be synced but just could not get cyl 4 to be close to the others. I will have to take off the tps switch and the choke switch as well and see if that changes. Im also having a hell of a time with the throttle cable connection to the chain and geared wheel that connects to the throttle Puccini wrote:

@Point-Seven-five wrote:Mass Air Flow sensor.

It's in the air box above the filter and tells the engine controller how much air and, by inference, oxygen is coming into the engine for combustion.

How reliable are they? I've got an 85 K100RT that idles and runs good for the most part but it has a unsettling habit of (every now and again) sputtering and stalling when your accelerating off of idle.
And very rarely at speed I'll get a short buck out of the engine

Usually in 1st gear. I did plugs, injector cleaning, wires, fuel filter. I understand the fuel pump was replaced just before I got it. Speedo shows 28K miles and I suspect it doesn't have more than 35K on it.
Cleaned the ignition switch, kill switch is ok.
Tried unhooking the TPS and no change.
replaced the fuel lines.
I thought it was vapor lock but it idles great even when it's really hot.
No indication of an electrical failure when it happens. All gauges stay on , no indicator lights,

I cleaned the tank bottom plug for the fuel pump so I think thats ok also.

I am installing the fuel line heat insulation wrap just to cover that base. But I am annoyed with this problem and want to fix it. Any Ideas?

RicK G · 12 Re: Cylinder balance at idle on Thu Mar 02, 2017 10:55 pm

RicK G

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Number of posts : 12303

@Puccini wrote:

@RicK G wrote:If the throttle bypass screws are set correctly and the bypass in the MAF then you will get minimal change screwing the throttle bypass out but it will change things if they are screwed in.

You totally lost me.

I don't understand what your trying to say.
Can you expand on it?

To get the correct setting on the throttle bypass screws and the MAF bypass you need to open the MAF bypass so as to let heaps of air in then set the throttle bypass screws with vacuum gauges or mercury manometer once they are set and the idle is at 950rpm (the vacuum reading is not important but they should be all the same) you then screw the MAF bypass screw SLOWLY until the engine falters then out SLOWLY till it picks up (about 1/4 turn) that way the barn door flap opens as soon as the throttle is opened.
If you are getting #4 not playing the game then I would suspect the butterflys are not synchronized. There are many threads that say DON"T TOUCH THE BUTTERFLY SETTINGS, that was all very well when they were near new but wear and tear makes it necessary.
You need to have them off the bike and set the backstop screw so that a piece of magnetic audio tape can just be drawn through the opening then adjust the rest till the same and back off the backstop screw till it hits the stop when the butterflys are closed fully and leave the backstop there as it is NOT an idle adjustment.
Idle speed adjustment is done by opening or closing the throttle bypass screws.

Hope this helps

RicK G · 13 Re: Cylinder balance at idle on Thu Mar 02, 2017 10:58 pm

RicK G

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Number of posts : 12303

@Bekman wrote:

I'm in exactly the same boat you are with my bike and it's very frustrating.when chasing down the problem I found I had low compression of 100 psi per cyl and was able to find a good used engine for a good price. It was cheaper for an engine than to get the head done etc. when i first started it, it ran great. Then it reverted to its old self which made me chase manifold leaks etc. had fun with those Oekiter clips, bought the wrong throttle cable, but was smart enough to buy the proper hose clamps on McMaster Carr as a backup. Basically lit $100 on fire. But who are we kidding. We love spending money on motorcycles. I adjusted with vacuum gauges the throttle linkage screws. I was able to get 1,2 & 3 cylinder to be synced but just could not get cyl 4 to be close to the others. I will have to take off the tps switch and the choke switch as well and see if that changes. Im also having a hell of a time with the throttle cable connection to the chain and geared wheel that connects to the throttle Puccini wrote:

@Point-Seven-five wrote:Mass Air Flow sensor.

It's in the air box above the filter and tells the engine controller how much air and, by inference, oxygen is coming into the engine for combustion.

How reliable are they? I've got an 85 K100RT that idles and runs good for the most part but it has a unsettling habit of (every now and again) sputtering and stalling when your accelerating off of idle.
And very rarely at speed I'll get a short buck out of the engine

Usually in 1st gear. I did plugs, injector cleaning, wires, fuel filter. I understand the fuel pump was replaced just before I got it. Speedo shows 28K miles and I suspect it doesn't have more than 35K on it.
Cleaned the ignition switch, kill switch is ok.
Tried unhooking the TPS and no change.
replaced the fuel lines.
I thought it was vapor lock but it idles great even when it's really hot.
No indication of an electrical failure when it happens. All gauges stay on , no indicator lights,

I cleaned the tank bottom plug for the fuel pump so I think thats ok also.

I am installing the fuel line heat insulation wrap just to cover that base. But I am annoyed with this problem and want to fix it. Any Ideas?

I would suspect that 100psi on each cylinder that the reading was done with the throttle closed where it should be wide open. 100psi is usually where the reading is when that happens.

Bekman · 14 Re: Cylinder balance at idle on Fri Mar 03, 2017 12:13 am

Bekman

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Number of posts : 69

Hi,

100 psi is in the poor rating for an engine. It was done at WOT and closed with not that drastic of a difference. 160psi is a good reading for compression.

Bekman · 15 Re: Cylinder balance at idle on Fri Mar 03, 2017 12:15 am

Bekman

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Number of posts : 69

My apologies about that first post. Something went a miss when quoting and being on my iPhone.

RicK G · 16 Re: Cylinder balance at idle on Fri Mar 03, 2017 12:38 am

RicK G

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Not hard to have an I phone do that Laughing

charlie99 · 17 Re: Cylinder balance at idle on Fri Mar 03, 2017 2:48 am

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measure your plug leads ...with plugs fitted ...electrode to electrode
I'm talking about through the coil as well ,,,so you should get a result close to 20,000 ohms ...depending on the leads you have fitted ...compare the two sets of measurements ...1 to 4 ...and 2 to 3 ... if there are differences explore further .

I have just recently thrown away poor plug leads because the corrosion of the plug tops had just become to great .(the previous owner had been running the right plugs ...but without the plug top ferules ...that make contact to the plug lead internal connectors....this caused massive pitting of the connector ...my attempts cleaned it up for a while, but the damage was already done ) ..affecting the idle drastically

I will say that I didn't notice too much losses at speed ...but every now and again it did miss ...scaring the crap out of me when the cam chain did a hiccup noise .

the low compression sounds like exhaust valve - seat pitting to me ....

good luck

Puccini · 18 Re: Cylinder balance at idle on Fri Mar 03, 2017 7:38 am

Puccini

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Number of posts : 89

I did replace the plugs and wire set so thats not a problem.

I did make one mistake. I adjusted the throttle stop assuming it was an idle adjustment.
How to I correctly reset the throttle stop?

I can't find any info on that.

RicK G · 19 Re: Cylinder balance at idle on Fri Mar 03, 2017 8:42 am

RicK G

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Number of posts : 12303

To get the correct setting on the throttle bypass screws and the MAF bypass you need to open the MAF bypass so as to let heaps of air in then set the throttle bypass screws with vacuum gauges or mercury manometer once they are set and the idle is at 950rpm (the vacuum reading is not important but they should be all the same) you then screw the MAF bypass screw SLOWLY until the engine falters then out SLOWLY till it picks up (about 1/4 turn) that way the barn door flap opens as soon as the throttle is opened.
If you are getting #4 not playing the game then I would suspect the butterflys are not synchronized. There are many threads that say DON"T TOUCH THE BUTTERFLY SETTINGS, that was all very well when they were near new but wear and tear makes it necessary.
You need to have them off the bike and set the backstop screw so that a piece of magnetic audio tape can just be drawn through the opening then adjust the rest till the same and back off the backstop screw till it hits the stop when the butterflys are closed fully and leave the backstop there as it is NOT an idle adjustment.
Idle speed adjustment is done by opening or closing the throttle bypass screws.
Making sure the butterflys are synchronized should be the first thing as that can and usually does affect the idle adjustment.

Bekman · 20 Re: Cylinder balance at idle on Fri Mar 03, 2017 11:43 am

Bekman

Silver member

Number of posts : 69

In all honesty the do not touch throttle plate screws can be touched. All carbureted bikes have them as well and after 20 + years things happen and it can become out of adjustment.

Things like the do not touch, must be serviced by BMW and the one time use Oekiter clips are a mix of good intentions, over engineering and most importantly making sure you go to the dealer to get serviced $$$. Which i understand when the bike is relatively new but it's not 1985 anymore.

He is going to need some vacuum gauges or mercury gauges to sort out his carb balance issues.

In regards to my bike, the engine in question with 100 psi has been swapped out. It was cheaper to get a known used engine. The only reason for me providing that information is that the bike is still suffering from the same symptoms.

Bekman · 21 Re: Cylinder balance at idle on Fri Mar 03, 2017 11:45 am

Bekman

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Number of posts : 69

The same symptoms being what the OP has stated

Bekman · 22 Re: Cylinder balance at idle on Fri Mar 03, 2017 5:07 pm

Bekman

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Number of posts : 69

Ok so in regards to my problem it looks like the throttle body shafts need to be rebushed. When spraying starter fluid it becomes blatantly obvious they are the problem. Does anyone have experience in re bushing the throttle shafts?

Point-Seven-five · 23 Re: Cylinder balance at idle on Fri Mar 03, 2017 5:18 pm

Point-Seven-five

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Number of posts : 2502

I can't recall what model or year your bike is. Can you post it in your signature?

Regarding your throttle bodies: I would suggest that it would be a lot easier to just replace them with a set with lower miles. There are lots of bike breakers on eBay who sell these throttle bodies.

Bekman · 24 Re: Cylinder balance at idle on Fri Mar 03, 2017 5:52 pm

Bekman

Silver member

Number of posts : 69

Yea I called two different shops close by to me and we came to the same conclusion. Just need to find a set with confirmed lower miles.

1 Cylinder balance at idle on Thu Mar 02, 2017 10:59 am

Puccini

2 Re: Cylinder balance at idle on Thu Mar 02, 2017 11:22 am

Point-Seven-five

3 ??? on Thu Mar 02, 2017 11:44 am

Puccini

4 Re: Cylinder balance at idle on Thu Mar 02, 2017 12:08 pm

Point-Seven-five

5 Re: Cylinder balance at idle on Thu Mar 02, 2017 12:25 pm

Puccini

6 Re: Cylinder balance at idle on Thu Mar 02, 2017 12:48 pm

Point-Seven-five

7 Re: Cylinder balance at idle on Thu Mar 02, 2017 1:56 pm

Puccini

8 Re: Cylinder balance at idle on Thu Mar 02, 2017 2:58 pm

Dai

9 Re: Cylinder balance at idle on Thu Mar 02, 2017 7:22 pm

RicK G

10 Re: Cylinder balance at idle on Thu Mar 02, 2017 9:12 pm

Puccini

11 Re: Cylinder balance at idle on Thu Mar 02, 2017 10:18 pm

Bekman

12 Re: Cylinder balance at idle on Thu Mar 02, 2017 10:55 pm

RicK G

13 Re: Cylinder balance at idle on Thu Mar 02, 2017 10:58 pm

RicK G

14 Re: Cylinder balance at idle on Fri Mar 03, 2017 12:13 am

Bekman

15 Re: Cylinder balance at idle on Fri Mar 03, 2017 12:15 am

Bekman

16 Re: Cylinder balance at idle on Fri Mar 03, 2017 12:38 am

RicK G

17 Re: Cylinder balance at idle on Fri Mar 03, 2017 2:48 am

charlie99

18 Re: Cylinder balance at idle on Fri Mar 03, 2017 7:38 am

Puccini

19 Re: Cylinder balance at idle on Fri Mar 03, 2017 8:42 am

RicK G

20 Re: Cylinder balance at idle on Fri Mar 03, 2017 11:43 am

Bekman

21 Re: Cylinder balance at idle on Fri Mar 03, 2017 11:45 am

Bekman

22 Re: Cylinder balance at idle on Fri Mar 03, 2017 5:07 pm

Bekman

23 Re: Cylinder balance at idle on Fri Mar 03, 2017 5:18 pm

Point-Seven-five

24 Re: Cylinder balance at idle on Fri Mar 03, 2017 5:52 pm

Bekman