The bypass valve "bypasses" the throttle plate. If the valve is open all
the time then in effect the throttle will not close. Blanking the bypass
"closes" the throttle. I have had some success cleaning and reinstalling
the bypass.
Sam
At 05:39 AM 6/16/99 -0700, john donohoe wrote:
>
>Um, I've fully rebuilt the ZS emission carbs on my GT6+, and the only
>way I could get the idle down was by blanking off those bypass
>valves...
>
>Can you explain why blanking the bypass valves helps the high idle
>problem, and also suggest what the *real* problem might be? Blanking
>the valves works great for me, but it seems to be a "work-around" and I
>would much prefer to solve the root problem!
>
>--- Atwell Haines <carbuff@nac.net> wrote:
>>
>> John,
>>
>> You may be the 'victim' of multiple problems.
>>
>> Now that the choke is out of the picture, it sounds
>> as if the
>> bypass/deceleration valve is bad. That's a common
>> cause of a 2000 to 2500
>> RPM fast idle.
>>
>> Got any gasket material left over? Blank that b/d
>> valve off and see if
>> your idle returns to normal...
>>
>> BTW if you are looking at the Bentley manual, be
>> advised that the pic of
>> the idle speed screw is misleading. The
>> spring-biased 'idle' screw is for
>> the _choke's_ fast idle; the actual idle screw is
>> the slotted headless
>> screw just forward of the other one. It has a 3/8
>> locknut surrounding it.
>> (This drove me bonkers for a while last year during
>> my 'learning' phase.)
>> Back that off before you muck with the bypass valve.
>>
>> You won't mess anything up by covering all the choke
>> holes with your
>> blanking gasket. And no, I don't know why they want
>> the throttle propped
>> open, unless its to make removing the choke's
>> linkages easier.
>>
>> Atwell Haines
>> '79 Spitfire, converted to manual choke, no beer
>> cans used at all.
>> Succasunna, NJ USA
>>
>> "When everything's coming your way, you're in the
>> wrong lane, going the
>> wrong way."
>>
>>
>>
>> At 04:53 PM 6/15/99 -0700, John Weale wrote:
>> >
>> > In my quest for a smog certificate, I blanked off
>> the water
>> >controlled choke in my Spit (using some gasket
>> material, though I was
>> >sorely tempted to use a bit of beer can just for
>> the heck 'uv it). Now
>> >the idle is around 2400 rather than the 1100 it
>> started at. I adjusted it
>> >down via the throttle speed screw, but am concerned
>> that I screwed
>> >something up. When removing the water choke, I did
>> not hold the throttle
>> >plate open as the manual (dug out after I did it of
>> course) instructs.
>> >Any idea why it says to do this? Is it reasonable
>> to hope that the choke
>> >was stuck open and blanking it off simply fixed the
>> mixture (it did fail
>> >smog due to high CO and HC's perhaps this
>> contributed?)(hey, I can dream
>> >:), raising the RPM's? Is blanking off all the
>> holes between the carb and
>> >water choke OK (I assume so, but that's gotten me
>> into trouble before)?
>> >
>> >Thanks for any advice!
>> >
>> >John Weale
>>
>>
>
>
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