Oilhead Tech Pages


Throttle synching for R1100's

Jon Diaz


How To Synch Those R1100 Throttle Bodies!

As an R1100 pilot, you've likely felt it: that little hum in the turn signal switch or the vibrating mirror you can't see out of or worst case, a bike that surges so badly at part throttle you can't ride smoothly. It's all part of those first days of R1100 ownership, and fortunately, very easy to deal with.

When you twist the R1100 throttle, the cable actuates a cam plate on the left throttle body, and then crosses over unbroken to the right throttle body. The entire cable length tends to stretch during those first few months of use, and this is why the cylinders fall out of sync with one another at part-throttle settings and give you the aforementioned 'character building attributes.'

I purchased a mercury manometer (Carb Stix) from my local dealer to use for this procedure. It consists of rigid plastic tubes sitting in a reservoir of mercury at one end, with flexible hosing attached to the other end to plug onto the taps at the throttle bodies. You will also need a 10mm box-end wrench, a flat-blade screwdriver, and needle-nose pliers.

Temperature of the motorcycle engine is critical to the success of this operation. I like to run my bike for at least 15 minutes before returning to the garage to perform the operation. Too hot an engine is bad as well, so avoid excessive idling or traffic during your warm-up period. If it is really hot outside, use a room fan in front of each cylinder to provide a little cooling breeze and temperature stability.

After the warm-up ride, shut the bike off and place it on the centerstand. Remove the black plastic injector covers if your bike has them, remove the vapor recovery tubes from the bottom side of each injector body, and insert the hoses from the Carb Stix onto the exposed taps. Hang the Carb Stix from the garage ceiling with a bungee cord or something similar so you can see the mercury levels easily from the right side of the bike.

Then loosen the locknut on the cable adjuster on top of the right-side throttle body cable, because this is where you will make the part-throttle adjustment. There is no need to fiddle with the cable adjuster on the left-hand throttle body for this procedure.

Start the bike. The mercury should come up a few inches in each tube, and if they are at different levels, this indicates a different amount of air is being drawn by each cylinder. Using the brass bypass screws on the top rear of each throttle body, align the two levels. Small rotation (ie. less than half a turn) of the screws should be all that is required to achieve this.

NOTE: The brass bypass screws are the only screws you need to turn for the synching operation. Resist all temptation to adjust the throttle stop screws on the bottom side of the throttle bodies. If one were to mess with these and accidentally back them out too far, the throttle butterfly will close too much, and when the whole works cools down, the butterfly will jam in the throttle body......in other words, JUST DON'T DO IT!

Once the idle balance is set, you should do a part-throttle setting to ensure that the butterflies are opening identically. Using about 2500 rpm, hold the throttle grip open with one hand, and adjust the knurled portion of the right side throttle body cable adjuster with your other hand to align the mercury levels. When the levels are even, let the bike return to idle (checking alignment again!), and if all is well, shut the bike off.

After synchronizing at part throttle, tighten the locknut on the cable adjuster, making sure that the adjuster does not rotate with the locknut and mess up your adjustment. Sometimes it is easier to hold the knurled adjuster with the set of needle-nose pliers while you tighten the locknut with your 10mm wrench.

Congratulations, you have done your first throttle synch. Now go out and ride until you can't see out of your mirrors again.....

--
Jon Diaz
diaz@cae.cig.mot.com
Day: (708)632-2919
Nite: (708)697-6421


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R-Tech pages maintained by: John Petty for the original author(s) and the Internet BMW Riders
Last Update: 09 September 2010