Throttle sync issue

[greenrider]

1997 BMW R1100RT

I for the life of me cannot get the throttle bodies synchronized!

The left side is always drawing a lot more than the right side no matter what I do.

I start with the left side screw turned out one and a half rounds.

No matter how I turn the right screw it doesn't even get close.

If I turn the left screw in to drop the idle, things just get worse.

The throttle cables are all loose.

 

Help would be greatly appreciated and thanks in advance.

[dirtrider]

1997 BMW R1100RT

I for the life of me cannot get the throttle bodies synchronized!

The left side is always drawing a lot more than the right side no matter what I do.

I start with the left side screw turned out one and a half rounds.

No matter how I turn the right screw it doesn't even get close.

If I turn the left screw in to drop the idle, things just get worse.

The throttle cables are all loose.

 

Evening greenrider

 

What does drawing more mean? Higher vacuum or more air (lower vacuum).

 

Have you removed the BBS screws & cleaned the tips & cleaned the air passages under them? If not then you probably need to do that so you can get good & proper air by-pass flow. (use o2 safer carb cleaner)

 

Are you trying to set just the base (at idle balance or above idle balance or both?)

[greenrider]

Answers to your questions DR

 

This is at idle speed, need to get this right first.

 

When I say it's drawing more, I mean more vacuum, the oil on my home made thing is two feet higher on the left side. That is with left TBS out 1-1/2 turns and the right side all the way in.

 

I did get it leveled out a bit closer now, the left TBS turned out 4 rounds and the right TBS cracked open less than quarter round.

 

No I didn't remove and clean the screws and clean. I will do this next.

[Michaelr11]

Important to clean the air bypass screws and passages - get it done. But, the right side not reacting much to changes in the position of the bypass screw would hint to me that you have some other source of air getting through to the engine. Could you have an air leak at any of the fittings at the throttle body?

 

How many miles on the bike?

 

Could your right side throttle body need a replacement shaft?

[greenrider]

144000 km on the bike.

I will check it for air leaks as well.

Is the shaft the most common place for air leak?

[roger 04 rt]

An air leak is a possibility. It could be at the shaft or possibly the gasket between TB and cylinder head.

 

Another is that the right-side TB is not firmly against the throttle-stop screw. Did you relax all the adjusters before trying to sync at idle?

[dirtrider]

Answers to your questions DR

 

This is at idle speed, need to get this right first.

 

When I say it's drawing more, I mean more vacuum, the oil on my home made thing is two feet higher on the left side. That is with left TBS out 1-1/2 turns and the right side all the way in.

 

I did get it leveled out a bit closer now, the left TBS turned out 4 rounds and the right TBS cracked open less than quarter round.

 

No I didn't remove and clean the screws and clean. I will do this next.

 

 

Morning greenrider

 

That is a good base starting point as those need to be clean before moving on. If after cleaning the BBS screws & passages you still can't get the cross side vacuum fairly even with close to the same BBS screw settings then move on & check for the R/H throttle shaft to be worn at the outer bushing, or the R/H throttle plate not closing properly (ie TB cam SOLIDLY on the base idle screw at idle), or the throttle plate has shifted position on the shaft, or the boot between the TB & the cylinder head is not leaking air.

 

If a high mile bike then a fair chance the R/H throttle shaft is worn at the outer bushing & leaking some air there.

 

You didn't mention checking/adjusting the valves first but that should be done/checked first as valve setting can effect the base idle cross side vacuum.

[Christo]

Sorry if this is a dumb question, but you didn't specifically say. Did you start with both screws unscrewed the same amount? If so, I would take the advice above and clean them both thoroughly by unscrewing and using some sort of solvent, and try again.

 

I just synched my throttle bodies yesterday a few minutes before you put up this post and didn't have any trouble. I also use a homemade manometer which consists of a long section of 1/4" tubing with 2-stroke oil in it, attached to an upright stand that forms a 'u' in the tubing, and the ends of the tubes plugged into each throttle body.

 

I can simulate the same effect you're having by screwing one of the BB screws all the way in. At that point the oil in the tubes very quickly becomes about a foot or two different from each other. And once the fluid levels get way out of balance, I quickly shut off the bike or my manometer will get fouled up. And even with the bike off, the only easy way to get them to equalize is to disconnect one of the hoses and suck or blow to level the fluid, then start again.

 

 

 

[greenrider]

 

I removed the right hand throttle body and cleaned it.

 

I am convinced its not a worn shaft that is the problem. I think the butterfly doesn't close far enough. It goes against the stop screw but doesn't seal the way I think it should. I turned the stop screw out 2 rounds and its much better. I can turn it out 4 rounds before it doesn't hit the stop screw.

 

What the proper way to setup the stop screw?

I know! I read that you don't mess with the stop screws but I don't know the history of this bike and don't know if somebody else might have.

 

 

And yes I did setup the valves before I started to do the sync.

[kalali]

I didn't think the butterfly valve should completely seal the TB with the shaft resting against the stop screw. If it did, the bike would not idle.

[T.M. Roe]

Just curious, does your 97 have a single cable that goes to one throttle body with a single cross over cable (early model) or the version that uses the junction box?

[Trobinson]

I didn't think the butterfly valve should completely seal the TB with the shaft resting against the stop screw. If it did, the bike would not idle.

 

Kalali,

 

You would be partially correct. The throttle is supposed to be open very slightly, perhaps .5 degrees (I believe this is correct for the 1100RT). You could compensate for fully closed butterflies by opening the bypass screws more, but then your throttle response will be poor as the butterflies will likely stick at closed position. The engine will idle, but launch or any other time you come off fully closed is going to have significant lurching.

[greenrider]

This is what I did.

 

Checked for wear. Didn't remove the shaft but there was no play or movement.

Cleaned the throttle bodies with carb cleaner.

Both left and right screws turned out 1-1/2 rounds.

Made sure both sides were against the stop screws.

Warmed the engine.

Had at least 2ft of difference.

Turned the right stóp screw out almost 2 rounds to level it out.

Then fine tumed with the brass screws

Then synchronized for high rpm.

 

I am very happy.

 

Now when the snow goes away I will try it out the road.