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09-17-2022, 11:10 AM | #1 |
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Join Date: May 2022
Posts: 2
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Idle speed too fast
FIXED
I just purchased a rebuilt zenith carb for my 1930 coupe, installed new intake and exhaust gaskets to very clean flat surfaces. The engine starts and runs really good but the idle speed is too fast, I have the idle speed screw backed out all the way. Even with the throttle linkage disconnected to make sure the throttle plate is fully closed I can't get the idle any slower. Last edited by Gschwab; 09-18-2022 at 07:28 AM. |
09-17-2022, 11:35 AM | #2 |
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Join Date: Jun 2010
Location: Temecula, CA
Posts: 4,092
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Re: Idle speed too fast
Check all gaskets for leaks, could be it is sucking air from somewhere other than the carb. You also might remove the carb and look at the butterfly to see if it is closing as it should, and maybe try a different carb.
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09-17-2022, 12:56 PM | #3 |
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Join Date: Apr 2011
Location: Davenport, Iowa
Posts: 2,113
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Re: Idle speed too fast
Separate the two halves, hold the upper half up to the sky or a strong light. With the throttle closed and the idle screw backed way off, you should not a see any light around the circular throttle plate, or if you do see light, it should be a consistent NARROW gap all the way around the circumference of the throttle plate. If one side shows more light than the other, the throttle plate is misaligned. If you do see too much light, then loosen the two throttle plate screws and wiggle the plate within its shaft until you reach a place where the light doesn't shine past the plate or it is consistently narrow all the way around. Of course, ideal would be no light. Once the plate is centered, tighten the screws and recheck that the plate didn't shift while tightening the screws. Sometimes when rebuilding the carburetors, guys don't spend enough time centering the throttle plate in its shaft.
Also, open the throttle plate all the way and examine the bevel on visible side of the plate. It has to close with the bevel sealing against the carb's throat. It's possible to put that plate in upside down so that it doesn't seal, allowing too much air to pass through the throat. This will also affect the idle. Marshall |
09-17-2022, 02:05 PM | #4 |
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Join Date: Apr 2021
Location: Central Illinois
Posts: 496
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Re: Idle speed too fast
X2 all the above.
Don't forget the wiper connections all the way to the wiper motor. It's gotta be getting air from somewhere???
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09-17-2022, 02:59 PM | #5 |
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Join Date: Jul 2010
Location: United Kingdom
Posts: 1,444
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Re: Idle speed too fast
All of above. Also 1) Sometimes the idle air mix screw does not seal very well- the tapered end of the screw gets worn as does the the orifice in the carb where it seats. ... that could be making the idle mix weak and 2) check the spring and cap of the idle mix screw are not preventing it from being screwed in sufficiently ...( I have had to shorten these on several carb rebuilds)
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09-18-2022, 07:30 AM | #6 |
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Join Date: May 2022
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Re: Idle speed too fast
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Sure enough the throttle plate was off center and not closing. She runs and idles great now! Thanks again for the help |
09-18-2022, 12:00 PM | #7 |
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Join Date: Apr 2011
Location: Davenport, Iowa
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Re: Idle speed too fast
Marshall |
09-18-2022, 01:15 PM | #8 | |
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Location: Germantown,TN
Posts: 518
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Re: Idle speed too fast
Quote:
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09-19-2022, 10:31 AM | #9 |
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Join Date: Jun 2015
Location: Red Deer, Alberta
Posts: 5,046
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Re: Idle speed too fast
Doesn't say good things for the rebuilder.
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