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Old 11-07-2003, 09:07 AM
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What's the proper idle speed

What's the proper idle speed for an SBC 400 with HEI? Right now it idles in park at around 1000 RPM. I was read something last night about HEI's changing dwell over 800 RPM. Also would to high an idle cause dieseling?

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Mark

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Old 11-07-2003, 09:18 AM
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I don't know your setup, but 1000 is high, 7-800 should be good, and it will cause dieseling if the throttle plates are open too much. possible vac. leak?
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Old 11-07-2003, 11:41 AM
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i have a 400 also...when the truck heats up the rpm will rise, when i start it it idles in park at like 900. when i put it into drive it will drop to like 600 before i give it some gas,
but when it warms all the way up in park it will be like 1500 and in drive it will drop to 1000.
is that a vacum leak??
and is that doing the same thing as yours???
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Old 11-07-2003, 12:00 PM
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My 355 Chevy was idling bad and I tried to correct it by fiddling with the carb.Today I took the carb off (Q-jet) and put new gaskets, top and bottom on it.Then I adjusted it with a vacuum gauge,now it idles at 900rpm in neutral and 750rpm in drive.The vacuum is steady at 21 in neutral and 18 in drive.
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Old 11-07-2003, 12:05 PM
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I wasn't implying it was a vac. leak, just a possibility. Many factors affect idle speed, timing, vac., carb settings, all need to be checked, all adjustments should be made with the eng at operating temps.
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Old 11-08-2003, 12:10 AM
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Well I went out and started checking some stuff out on the carb. First I let the engine get up to temp. I noticed the choke plates (Electric Choke) were not completely opening, so out can the screw driver and I re-adjusted it so they were totally vertical when the engine is at temp. Then I decided to check the carb and 2 of the bolts were a little on the loose side. They are not now. One thing is the Q-jet seems to be a little inconsistent on idle speed. Bump it by hand and it will one time come down to 800 then the next bump it might stay at 1000. Any ideas? Should I lube the accelerator linkage and wire. also should you lube the bushings?

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Mark
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Old 11-08-2003, 02:05 AM
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I would still change those gaskets to be sure.The three screws on the under side of my carb were also loose.Once the gasket has been wetted by fuel it is usually useless.
Keeping all those screws tight is an never ending job,also the four bolts that hold the carb loosen up.Iīm not sure if I should use some type of thread locker, and the fine thread in the carb body strips so easily.
But if your getting inconsistant idle speeds there must be a leak.
The linkage should be clean and dry, and maybe you need to rebush the throttle shafts.I did mine with a kit from Jet.
Is the return spring working properly,maybe itīs tired.
The throttle cable should not be lubricated.
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Old 11-09-2003, 12:11 AM
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800 neutral, 650 in drive (approx)
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