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Holly power valve #1794393 04/01/15 06:38 PM 04/01/15 06:38 PM
Joined: Jul 2008 Posts: 221 New Mexico, USA A attaboy OP enthusiast
attaboy OP enthusiast A Joined: Jul 2008 Posts: 221 New Mexico, USA	My 71 Charger w/440 & 750 Holly carb seemed to backfire when I started it the other day. Since then the regular 1000 rpm idle reading dropped to 800 rpm. The idle is much rougher. There isn't as much as before. Do these sound like the symptoms of a bad power valve? What does a blown one look like? Thanks

Re: Holly power valve [Re: attaboy] #1794394 04/01/15 06:48 PM 04/01/15 06:48 PM
Joined: Jun 2006 Posts: 5,162 CT GTX MATT master
GTX MATT master Joined: Jun 2006 Posts: 5,162 CT	How old is the carb? Is it now rich at idle? The newer Holley's wont blow the PV on a backfire. If you take it out the rubber diaphragm on it would be ruptured. You may have another issue which caused the backfire. Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street

Re: Holly power valve [Re: GTX MATT] #1794395 04/01/15 08:38 PM 04/01/15 08:38 PM
Joined: Jul 2008 Posts: 221 New Mexico, USA A attaboy OP enthusiast
attaboy OP enthusiast A Joined: Jul 2008 Posts: 221 New Mexico, USA	I'd guess that it's maybe 5 years old or so. May be something else, I don't know. Never did that before. I'm guessing a backfire. There was a "pop" when I stared it. Never made that sound before so I'm guessing a backfire. Whatever it was, the always consistent 1000 rpm idle went to 700 rpm. That's the new "norm". Doesn't idle the same either. The idle is much rougher. Checked plug wires, etc. They look good. I'm going to let it warm up and then spray some break cleaner all around the intake to see if there is a vacuum leak there causing the symptoms. Sounds like the power valve is a pretty easy to check. Should be easy to spot if it's bad. I have never seen a bad one so I wasn't sure what to look for. Now I know so I'll check.

Re: Holly power valve [Re: attaboy] #1794396 04/01/15 08:57 PM 04/01/15 08:57 PM
Joined: Jun 2006 Posts: 5,162 CT GTX MATT master
GTX MATT master Joined: Jun 2006 Posts: 5,162 CT	Yeah easy to check, being that new it should have the blow out protection, although I believe I've heard people claim it will still pop them, I've never had an issue. Check your air bleeds for crud too. This a points car, or electronic ignition? Has it sat all winter? You'll know more when you get the primary bowl/metering block off. Last edited by GTX MATT; 04/01/15 09:03 PM. Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street

Re: Holly power valve [Re: attaboy] #1794397 04/01/15 09:25 PM 04/01/15 09:25 PM
Joined: May 2008 Posts: 5,399 Aurora, Colorado 451Mopar master
451Mopar master Joined: May 2008 Posts: 5,399 Aurora, Colorado	Being a "Holly" carb it may need some water to grow.

Re: Holly power valve [Re: GTX MATT] #1794398 04/01/15 11:26 PM 04/01/15 11:26 PM
Joined: Jan 2003 Posts: 9,436 Blair County,PA 62maxwgn master
62maxwgn master Joined: Jan 2003 Posts: 9,436 Blair County,PA	Quote: Yeah easy to check, being that new it should have the blow out protection, although I believe I've heard people claim it will still pop them, I've never had an issue. Check your air bleeds for crud too. This a points car, or electronic ignition? Has it sat all winter? You'll know more when you get the primary bowl/metering block off. Something to think about! 8478232-PA260598.JPG (42 downloads)

Re: Holly power valve [Re: attaboy] #1794399 04/02/15 12:02 AM 04/02/15 12:02 AM
Joined: Nov 2003 Posts: 3,428 Dandridge TN D Dabee master
Dabee master D Joined: Nov 2003 Posts: 3,428 Dandridge TN	Sounds like the PV to me. PVs are cheap and easy to change. Throw a new one in and see if it fixes the problem. If not then start doing the other trouble shooting stuff suggested.

Re: Holly power valve [Re: 451Mopar] #1794400 04/02/15 03:54 AM 04/02/15 03:54 AM
Joined: Jul 2008 Posts: 221 New Mexico, USA A attaboy OP enthusiast
attaboy OP enthusiast A Joined: Jul 2008 Posts: 221 New Mexico, USA	Hey 451 Guy. Spoken like a true Fool Injection guy. Last edited by attaboy; 04/02/15 03:56 AM.

Re: Holly power valve [Re: GTX MATT] #1794401 04/02/15 03:59 AM 04/02/15 03:59 AM
Joined: Jul 2008 Posts: 221 New Mexico, USA A attaboy OP enthusiast
attaboy OP enthusiast A Joined: Jul 2008 Posts: 221 New Mexico, USA	It's been converted to electronic ignition. I usually drive it several times in the winter if the weather is nice. This is the first time it ever made that "pop" sound on startup.

Re: Holly power valve [Re: attaboy] #1794402 04/02/15 02:09 PM 04/02/15 02:09 PM
Joined: Jan 2003 Posts: 16,376 D dogdays I Live Here
dogdays I Live Here D Joined: Jan 2003 Posts: 16,376	IF you can run your idle mixture screws all the way in and the engine still runs, it's most likely the power valve. They are so inexpensive that I'd replace it just on principle, if the fuel bowl is coming off. R.

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