Throttle Synch Issue?

[BMW_Ken]

Bike is a 2004 R1150RT.

I just rebuilt my left throttle body replacing the o-rings, shaft, and bushings. Did a valve check and then used the GS-911 to set the throttle position sensor.

I made sure the cables were loose allowing the throttle bodies to be on the idle stops. I used the Harmonizer electronic synch instrument and double checked with the Twin Max. The issue is that that to get a balanced idle the brass air bleed screw on the left throttle body is barely off the seat and the right one is out about .75 of a turn giving me an idle of about 1200 rpm. I cannot get an idle speed any lower without having the left bleed all the way in and this is still only about 1175-1200 rpm with a good balance.

The good thing is the rattle from the left throttle body is gone due to the rebuild and the engine is smooth.

 

Why can't I get the RPM down to 1100rpm with good balance per the BMW spec?

 

Thanks.

[dirtrider]

Evening Ken

 

It sounds like you don't have the throttle plate properly centered in the throttle bore. Or you don't have the throttle idle stop screw set correctly.

 

The throttle body idle stop screw is set by the manufacturer using air flow/throttle plate angle (something you can't easily duplicate).

 

I'm not sure you can get that throttle plate centered correctly with the throttle body still mounted on the bike.

 

In any case you need to try to do a better job of centering the throttle plate in the throttle bore. The way I do it is to first MARK THE IDLE STOP SCREW for EXACT position. Then back it out until it has a decent gap & isn't contacting the throttle cam. Then loosen the throttle plate screws a bit. Now hold the throttle body up to a strong light & play with the throttle plate until it is evenly centered in the throttle bore with it tightly closed. Then re-tighten the throttle plate screws.

 

Now put the idle stop screw back where it was. Re-install the TB & re-check the TPS. (personally on the 1150 learnable TPS I use actual TPS voltage rather than the GS-911). But in any case get a TRUSTED base TPS setting around .365-.385 volts.

 

Then do a new TPS re-learn after installing the throttle body (be sure the choke is OFF).

 

Then see what you get for base hot curb idle & TB balance. If you still can't get a proper base hot curb idle with the BBS where you need it then set the BBS to nominal spec & use the L/H idle stop screw to see if you can get what you need. You will have to keep on the TPS setting as you adjust the idle stop screw as moving that screw will change your TPS setting.

 

It could take a bit of fiddling but if you are persistent you should be able to obtain the correct base hot curb idle at a close BBS setting once the throttle plate is properly centered in the throttle bore.

 

[Peter Parts]

That is a super-helpful post from DR and anybody whose TBs ever got the darn zero=zero should study it carefully.

 

Naturally, I have my own take on this matter, although not anything I've actually tried with a TB.

 

Esp. for a guy who owns that nifty Harmonizer (which should put TwinMax out of business for sure), I'd try working with airflow. After all, air flow is the basic parameter (gold standard), not best-eyeball setting of mechanical parts.

 

Ben

[PAS]

Plus one on the Harmonizer. Nice tool!

[Alfred02]

Same

The Harmonizer is excellent and a child can drive it.

No Manual required as the few instructions you need, are on top of the case on the LHS.

Just another very happy customer.

[BMW_Ken]

Well, thanks to Dr and others, the synch issue is resolved.

I followed DR's instructions and now have perfectly balanced throttle bodies at 1100 rpm idle with the bleed screws at almost exactly the same setting. The off idle balance is perfect also. Engine is smoother than I ever remember it being.

 

This concludes my winter maintence: spline inspection and lube, gear position switch replacement, starter disassembly clean and lube, valve adjustment, throttle body rebuild and synch, and final drive oil replacement.

 

I'm ready for my trip to Daytona in a few weeks. Yahoo!!