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Re: Lets get back to oilheads... throttle body question
- Subject: Re: Lets get back to oilheads... throttle body question
- From: andrew johnson <sundiaL@xxxxxxx>
- Date: Fri, 2 Sep 2005 16:11:50 -0700
At 1:46 PM -0400 9/2/05, John Van Deren wrote:
>Today I was adjusting the throttle body synch on my 94 RS (110K
>miles) and noticed that the right brass air bypass screw needed to
>be almost closed (clockwise) to attain balance on the Twinmax. The
>left screw is a couple of turns out. I cannot get the idle low
>enough to suit me...about 1400 rpm is as low as I can get it. Does
>this indicate that the right throttle body has a problem (wear)? Do
>I have an air leak perhaps on one side? Any wisdom from the pros
>out there would be greatly appreciated. BTW, I use GS tubes.
>John Van Deren
>High and dry in Montpelier, VT
Could be an issue with your throttle body, the butterfly shaft can
wear and allow air to pass through its bore in the cast body.
Conventional wisdom says squirt carb cleaner on the throttle body
near the shaft's bearing points and see if any change in idle.
I finally tossed the TwinMax. It had developed a preference to lean
off to one side, indicated by swapping hoses and seeing a whole
different reading from the last set zero. I was also looking for
something better for adjusting the throttle stop screws.
I made up a water gage, about 28 feet of 3/16 I.D. vinyl tubing, in a
"U" shape along a four-foot wood board, with exactly the same lengths
from bottom of "U". I filled it with colored water to half the height
of the board. When I attach this to the vacuum ports I get a very
clear and stable indication of whether the engine is in balance or
My adjustment process is as follows:
1. Valves dead-on, cold, OVAD style with four guages, engine set at
TDC with home-built TDC flywheel locking tool.
2. Remove and clean the Big Brass Screws (BBS) and their bores with
carb cleaner. A faint dab of silicone grease on the O-ring, then back
3. With engine fully warmed up, and throttle cables slack against
their adjustment barrels, the BBS are fully and gently seated (turned
in clockwise until they stop).
4. Engine running (roughly and slowly) I adjust the right hand side
throttle stop screw until I have perfect balance in the water tubes
(or TwinMax). The water tubes take a while to settle, be patient.
When the engine is balanced at this stage, you will feel and hear a
discernable relaxing of the roughness, even though it's idling at 600
5. I back both BBS out two full turns, then adjust for balance at
idle (throttle cables still slack).
6. I finally adjust for off-idle balance by moving the right hand
side throttle cable adjustment barrel, as needed. Take it to 1500 RPM
for basic measurement, higher if you wish.
This is what I do. The left side throttle stop is fixed, TPS is set
at 0.390 volts, I don't mess on that side except BBS.
Bike runs so smooth now, the water gage helped me get the throttle
stops in perfect balance, as never before.
- - andrew, Berkeley, '00 R1150GS
- - "Moto per Mangiare, Mangiare per Moto"