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Re: Lets get back to oilheads... throttle body question
- Subject: Re: Lets get back to oilheads... throttle body question
- From: Bob Hadden <kbhadden@xxxxxxxxxxx>
- Date: Sat, 03 Sep 2005 07:47:12 -0400
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
>> 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.