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Old 06-01-2019, 08:55 PM
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Idle speed problem

After some down time for repairs and upgrades it seems like my carb doesn't want to come off the fast idle. The carb was turned pretty well before but it stays around 1500 rpms and the choke is only open half way even when it's warmed up.
It is a 350 with a Holley 80457. Seems to me that it might be the choke adjustment.

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Old 06-02-2019, 07:36 AM
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Your choke should open up all the way unless you don't have a full 12 volts going to it or your choke coil is worn out. Even if it opens up half way the idle should go down some but it never will all the way though unless you have it working right and adjusted correctly and there should be a little notch on the black coil cap and there are notches on the choke housing and if your turn the choke clockwise you lean it out and it will open up faster and if you turn it counter clockwise it will be richer and take longer to open up.



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Old 06-02-2019, 10:25 AM
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Thanks Eric I watched that video when I tuned it before and again yesterday. When I got the truck the choke was disabled and it didn't seem to be adjusting as easily as it does in the video. Once I got it right it was working correctly but I did suspect it was going bad. Would it be just the cap that needs replacing?
I got the transfer slots where they should be when I had it apart. Also went from 76 to 64cc heads. Would either of those require changes to the mixture screws or anything else? I just don't want to start randomly changing things and cause more problems.

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Old 06-02-2019, 11:37 AM
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If you swapped out your heads and your running more compression then you might have to readjust your idle mixture screws but that is something I have not done before on an engine build by just swapping heads out and nothing else but it would not hurt to readjust them. Use a vacuum gauge on full manifold and adjust them inward till you reach the highest vacuum then back them back out about a 1/4 of a turn as if you leave the idle mixture screws on the highest vacuum reading most of the time it will be a little to lean and it will stall once in gear. Start them out 1 and a half turns and start on driver side first moving them in a 1/4 of a turn on each side and you want to keep them equal.

And yes if your choke coil is going bad then all you would replace is the black cap part and you have to make sure it is on the choke tang as the heated coil element on the inside has a wrap around loop that goes over the tang that sticks out from the choke housing and you have to make sure it is on it or it will never open the choke and work.
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Old 06-02-2019, 12:37 PM
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That's pretty much what I was thinking about and it worked out. The choke was about 3 notches off and one of the mixture screws was only 1/4 turn out. I got max vacuum right at the base setting so they're both at 1 3/4 out.
Also I only had about 10" of vacuum with the old heads and now it's above 15 so I'm optimistic it'll be more streetable now.

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