[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Lets get back to oilheads... throttle body question

Thanks, Andrew,

I wish we could post photos.  If the 28 feet of tubing are in a "u" 
shape on the four foot board (using what sounds like about 10 feet of 
the tubing), where is the remainder of the 28 feet?  I'm having a little 
trouble visualizing what your vacuum gage looks like.  Anyway, I'll test 
for air leakage w/carb cleaner.  The tube clamps are tight. I do have an 
old Carb Stik w/mercury that I never liked.   I may break it out and see 
if I can adjust the throttle stops as you suggested.  I've never removed 
the BBSs and cleaned them so I'll do that too.  I had done a careful 
valve adjustment (OVAD).  The engine runs smoothly, but I'd like to 
determine why the BBSs are so uneven in their setting and get the idle 
down a bit.  Thanks for your ideas.

John Van Deren
Montpelier, VT

andrew johnson wrote:

> At 1:46 PM -0400 9/2/05, John Van Deren wrote:
>> Hi listers,
>> 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 not.
> 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 in.
> 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 
> RPM.
> 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.