throttle body adjustment

[DAM650]

the clymer manual states ALL R1150 models there is no synchronization process, must hook up to mo dit ec at the stealership for this procedure.

is this true, after I just built me a yard stick manometer and all?

[racurley]

Untrue. Manometer procedure well documented here and other sites. Hook your tubes to the vacuum nipples, start it, adjust the BBS to balance. Easy peasey. But, find the full description.

[peels]

I made my own. works fine.

its quite simple. just make sure you keep your engine cool.

[CycleRob]

DAM650,
The How-2-Adjust procedure is detailed in the middle of a water Manometer construction post here: http://r1150r.org/board/viewtopic.php?p=156874#p156874

FYI: BBAS=BigBrassAirScrews (The big screws on the TB with a screwdriver slot in the head)

[sstein]

I kinda wonder - is it really a synch procedure? "Synch" implies synchronize. If the BBASs adjust air flow during idle, there really is no timing adjustment occurring, right? More of a idle rich/lean matching procedure?
Granted, I am relatively uneducated regarding these matters.

[Sunbeemer]

You're right. "Synchronization" is probably a misnomer for a procedure that actually balances both cylinders' power outputs by equalizing the amount of air passing through the throttle bodies. The manometer measures the vacuum created by the venturi effect of air passing through the throats of the throttle bodies, and if it is the same for both, the amount of air inspired by each cylinder is considered equal, which should generate the same amount of combustion pressure in each cylinder, and thus the same amount of force on their pistons.

The big brass air screws (BBAS) are just air bypass bleeders that admit air into the cylinders when the throttle plates are closed and so only control cylinder combustion pressures at idle.

This is why it is important to equalize the manometer columns both at idle (by adjusting the BBAS's) and at higher rpms (by adjusting a throttle cable).

Does that clear it up?

[CycleRob]

Member sstein is correct when he asked "More of a idle rich/lean matching procedure?" The 2 BBAS fine tune the air flow to compensate for both throttle butterflies that are almost always not open the exact same amount while they are resting on the blue painted throttle stop screws. When the BBAS are used to properly set equal vacuum readings indicated by the water manometer, they precisely make the air flow into both cylinders exactly the same. Since both fuel injectors are supposed to inject the same amount of fuel mist, turning "in" (CW) a BBAS will make that cylinder mixture richer AND less filled with the air-fuel mixture.
We can see now how a high mileage bike may have both worn TB shafts/bushings, erratically leaking in differing amounts of "bypass"air as the throttle setting changes -and- fuel injectors with varying amounts of dried fuel deposits that now effectively do not inject the exact same amount of fuel per shot. Those 2 events can explain why the water columns behave erratically, repeatedly, when "on-throttle" and/or the engine occasionally idles rough, slower and/or at differing RPMs. The solution is to use a name brand detergent gasoline (I use Chevron/Texaco/Shell) and occasionally use a weak dose of fuel system cleaner. Also, if you see your TB cable pulleys moving and making tapping/clicking noises at an idle, it is time to have the shafts and bushings expertly replaced. Then, after a proper water stik synch, you will know what a new bike feels like . . . very smooth!

[DAM650]

thank you gentlemens for all your knowledge and concise replies

[sstein]

Yes, thanks. I have an early 1960s honda cub 50 and I am always struck by the amount of cylinder vacuum produced which can be easily appreciated by covering the carb air intake with the palm of my hand. Reinforces the importance of a clean air filter and airbox.