Scott,
Great info on the bypass valve, but if I remember correctly (probably
don't) screwing the adjustment screw IN (clockwise) actually reduces
the spring load on the valve and causes it to open under less pressure.
Do I have this right? What I really want someone to tell me is how to
make the adjustment. I have cleaned the assemblies and replaced the
gaskets in both my Spit and my TR6, but I've just been adjusting by trial
and error until things "feel" right.
Tim Gaines
1980 Spitfire
1974 TR6
>Ken:
>
>I'd almost bet your problem is with the by-pass valve. I also
>redid the temp compensator and even re-calibrated them
>which the manual says you can't do (there is a great write
>up on how to do this in the tech session of the VTR, and it
>works!). I too still had the high idle after this so moved on to
>the bypass valve.
>
>The high idle is caused by either a rip in the valve diaphram, which
>are made of rubber and eventually become brittle, or the valve is
>stuck open. Either way you will need to rebuild, or some people
>suggest just blocking off (i am not one). Does your bypass valve
>have an external adjusting screw? If it does, you may want to
>try screwing it in which will lower your idle if their isn't a leak/
>tear in the diaphram. Another easy test is to remove the bypass
>valve (you can do this with the carbs still attached to the
>manifold) and tape over the holes with some duct tape. If your high
>idle is caused by the stuck open valve or a leak, it will disappear
>by just eliminating the bypass channels from sucking air/fuel around
>the throttle. If you were like me and tried fixing the problem
>by adjusting the high idle via timing and slow idle screw, be sure
>to go back to a datum setting before trying this because this may throw
>you off with the carbs all out of wack!
>
>In essence, and quoted from the Haynes Tech book, "The by-pass valve
>provides a means of limiting the very high manifold depression
>which occurs when the engine is in the over-run condition." Thus,
>allowing the air and fuel mixture to be sucked into the manifold
>around the throttle disk when it is shut (let off of the gas peddle when
>running the engine, lets say at 60 mph) when the engine is running,
>allowing some degree of engine breaking without relying on only the idle
>set of the throttle. This is my best understanding but don't quote
>me, I'm still learning!
>
>If you need further help, let me know.
>
>Scott Suhring
>Elizabethtown, PA
>'70 TR6
>
>
>Beth and Ken wrote:
>>
>> Scott;
>>
>> I rebuilt my stuck (closed) temp. compensators, but I still have that high
>> idle/little braking situation. So, I'm thinking about those bypass valves.
>> If they are my problem, is it because they are stuck shut, allowing no air
>> to bypass, or would it be that they are stuck open (or leaking) allowing air
>> to pass when they should be shut?
>>
>> What is it they do when the car is hot...open or shut?
>>
>> Thanks,
>> ken
>
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