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

Hi Bob,

Yeah, I'll check TPS voltage too...haven't done that in a looong time.  
I was hoping to ride on this beautiful morning but I guess I have some 
work to do.  Thanks for your thoughts (and replacement TPS if I need it!).

John Van Deren
Montpelier, VT

Bob Hadden wrote:

> John,  The setting of the tps affects the idle speed.  Perhaps, with 
> the mileage on your bike, the throttle stop has loosened up or the tps 
> is wearing and not getting down to the proper level.  You should check 
> the throttle stop to be sure it is not loose, and check the tps 
> voltage to be sure it is still where you want it.
> Incidentally, I have a tps new in the plastic if you need it.
> Bob Hadden '05R12GS, '62R27
> On Sep 3, 2005, at 7:37 AM, John Van Deren wrote:
>> 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.