holley power valve issues - Vintage Mustang Forums

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post #1 of 9 (permalink) Old 05-18-2017, 08:34 AM Thread Starter
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holley power valve issues

We have a 66 coupe that we built up and the hypo motor has a holley street avenger carb on it with fuel pressure regulator and gauge. It had been running great but has been sitting for some time as my son has been deployed. Now it backfires upon acceleration blowing the power valve spewing gas all over the engine and it poses a serious fire hazard. I want to get it dialed in for his return in a few weeks. So what is causing this problem and what can I do to fix it?
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post #2 of 9 (permalink) Old 05-18-2017, 10:31 AM
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Generally, a Holley spews gas when the needle valve is not holding the fuel pressure. The newer Holleys have power valve protection, so I doubt it is blowing. Try dialing down the fuel pressure, and check the power valve to be sure.
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'67 coupe, 390-S, 4spd.
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post #3 of 9 (permalink) Old 05-18-2017, 11:09 AM
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Ethanol in the gas eats up the power valve and float needles. Time for a rebuild and switch to pure gas.
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post #4 of 9 (permalink) Old 05-18-2017, 03:52 PM
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Quote:
Originally Posted by Alan _MacDougall View Post
Ethanol in the gas eats up the power valve and float needles. Time for a rebuild and switch to pure gas.

This! Happened to my brand new street avenger after only a year. Didn't run it much and paid the price. Rebuild fixed the problem, though mine was just the power valve.


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post #5 of 9 (permalink) Old 05-18-2017, 04:13 PM
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There's no place for Ethanol in these older cars.... or my lawn mower for that matter! I try to stick with the straight stuff 91 octane when possible.
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post #6 of 9 (permalink) Old 05-18-2017, 04:53 PM
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Quote:
Originally Posted by Alan _MacDougall View Post
Ethanol in the gas eats up the power valve and float needles. Time for a rebuild and switch to pure gas.
over the years some friends with newer cars that sat for a few months had the in tank fuel pump go bad due to the ethanol in the gas. use an all metal needle and seat in your golley carb

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post #7 of 9 (permalink) Old 05-18-2017, 05:19 PM
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How good are the Street Avenger Holleys? Never tried one. I like that they have dual metering blocks and jetable secondaries.

'67 coupe, 390-S, 4spd.
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post #8 of 9 (permalink) Old 05-18-2017, 05:44 PM
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pERFER THE QUICK FUEL carbs these days more easly adjustable use several of them with no issues. Recomend using the alcohol proofed power valves, accelerator pump diaphragms from QF also.
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post #9 of 9 (permalink) Old 05-18-2017, 06:31 PM
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Originally Posted by maladezo View Post
How good are the Street Avenger Holleys? Never tried one. I like that they have dual metering blocks and jetable secondaries.
The only personal experience I have is with the 670 SA on a 4V Cleveland and then on a mild 460. They are generally calibrated a bit on the lean side and they have accelerator pump issues due to return spring interference with the pump lever.

Like anything else they can be made to work.

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