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Re: Lets get back to oilheads... throttle body question
- Subject: Re: Lets get back to oilheads... throttle body question
- From: John Van Deren <r11rider@xxxxxxxxxxx>
- Date: Sat, 03 Sep 2005 07:37:40 -0400
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
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
> 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.