Holley 390 Adjustment Help
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Senior User
Joined: Jan 2003
Posts: 327
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Holley 390 Adjustment Help
I just put a Holley 390 4 barrell on my 84 300. It is running really rich. It is blowing wet soot out the tail pipe. Also it stumbles when you press the gas quick. I'm new to Holleys, how do I fix it?
Thanks
Thanks
Postmaster
Joined: May 2002
Posts: 3,241
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From: Broken Arrow, OK
If by wet soot you mean black smoke the power valve is probably blown and dumping lots of gas into the engine. The fix for that is to take the front bowl off the carb and replace the PV. Before you do that measure your idle vacuum (in gear if it's an auto) and get a new PV that is at least 2"Hg lower than the idle vacuum. If it blew the valve from a backfire it would be a good idea to install a checkvalve kit in the powervalve vacuum channel to prevent it from doing it again. Many Holley's that were built in the last decade or so have this check valve from the factory. What usually happens is the carb has a lean hesitation off idle which causes a backfire through the intake and blows the valve. The root cause of this is usually too little secondary opening at idle which causes too much primary opening at idle. When the primaries are open too far they expose too much of the transition slots and screw up the transition from the idle circuits to the main metering system. The problem is usually band aid fixed with more accelerator pump because that requires less effort to do.
Elder User
Joined: Mar 2003
Posts: 628
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From: Colorado
Rejet your carb to your altitude. Stock - sea level is 51's, "go 1 size smaller for every "approximately" 2,000' above sea level" - according to the Holley instructions included w/my 390. You may have blown a power valve, but I've been running the same one for almost 7 months now, with no problems. Mine was 3-4 jet sizes too rich "out of the box". I had the same same symptoms you described. The idle mixture srew is just that - IDLE mixture. You MAY still have to adjust the carb to run a proper mixture at medium and full throttle.
Broncr
Broncr
Last edited by broncr; Nov 18, 2003 at 10:12 PM.
