Backfire on a 454

« **on:** July 24, 2012, 11:56:33 AM »

Had my rig out at El cap on Sunday all was working good but I had a slight backfire popping sound coming from my engine at wide open. Fuel pressure is at 6.5lbs and it's a new Holley 4150. Would that mean its too rich or lean? It was also lil sluggish out of the hole if I stood on it too hard it would stall. Would that mean the primary's are a lil rich?

« **Reply #1 on:** July 24, 2012, 12:12:45 PM »

More accelerator pump? I don't know Holleys... Mine pops if I jump on it too quick, but if I flick throttle before I mash it to give it an extra squirt.

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« **Reply #2 on:** July 24, 2012, 01:11:03 PM »

Could be electrical/ignition
check for -
vacuum leaks
plug wires burnt/ worn
carbon tracking in dizzy cap
cracked electrode on spark plugs
worn cam lobe/lobes
burnt valve/ bent pushrod
there could be more

Daniel

« **Reply #3 on:** July 24, 2012, 01:14:28 PM »

is it a backfire or a lean "pop"?

« **Reply #4 on:** July 24, 2012, 01:17:38 PM »

Could be a lean pop it's only a wide open throttle. I'm thinking the primary's are rich and the secondary's are lean.

« **Reply #5 on:** July 24, 2012, 01:49:35 PM »

Quote from: Santee_Native on July 24, 2012, 01:17:38 PM

Could be a lean pop it's only a wide open throttle. I'm thinking the primary's are rich and the secondary's are lean.

assuming your bowls are staying full, what are your jets set at? i was jetted too low and if i stood on it i would get a lean pop from the exhaust... almost like it was stuttering.

« **Reply #6 on:** July 24, 2012, 02:05:13 PM »

If I stand on it dies out. If I just ease into it all is fine until the very top end thats when it has a pop.

Like when I'm coming off plane I watch for the wake as soon it's time to goose it I do and it stalls out.

« **Reply #7 on:** September 30, 2012, 02:35:24 PM »

Did you ever get worked out? I have a chevy 350 doing the exact same thing.

« **Reply #8 on:** September 30, 2012, 06:12:11 PM »

Sounds like weak valve springs. They are not closing fast enough. In a new Holley with the correct fuel pressure it should be close with the jetting and most likely it will not be that lean. A carburetor only passes so much air. I have had this problem an it was valve springs.

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« **Reply #9 on:** September 30, 2012, 08:01:22 PM »

have you looked at the spark plugs??? they should be able to tell you something!

« **Reply #10 on:** October 01, 2012, 05:22:32 AM »

I would check your ignition system if thats a new holley. Timeing wires cap rotor etc. good luck.

« **Reply #11 on:** October 06, 2012, 05:29:42 PM »

check your timing, and advancement, if you're running a mallory unilight throw it away

« **Reply #12 on:** October 06, 2012, 07:35:21 PM »

Quote from: FSMMARINE on September 30, 2012, 06:12:11 PM

Sounds like weak valve springs. They are not closing fast enough. In a new Holley with the correct fuel pressure it should be close with the jetting and most likely it will not be that lean. A carburetor only passes so much air. I have had this problem an it was valve springs.

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Bingo! Problem solved!

Ray

« **Reply #13 on:** October 08, 2012, 11:51:22 AM »

Well it is the off season guess its time for a new top end and get rid of my peanut port heads. Any recommendations on a complete set up?

« **Reply #14 on:** October 08, 2012, 12:42:10 PM »

some 781 or 049 can be reasonable if in good condition, but if buying new, there is some good deals on aluminum heads too. then a single plane manifold (Eddy vic jr airgap, etc.) or tunnel ram, if $$ permits.
Might look into a cam upgrade too

Daniel

« **Reply #15 on:** October 08, 2012, 03:05:38 PM »

Quote from: FSMMARINE on September 30, 2012, 06:12:11 PM

Sounds like weak valve springs. They are not closing fast enough. In a new Holley with the correct fuel pressure it should be close with the jetting and most likely it will not be that lean. A carburetor only passes so much air. I have had this problem an it was valve springs.

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Thats my 1st thought...or a valve thats just set too tight...or both.

Santee_Native

Backfire on a 454

BIG JOHNSON

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ka0tyk

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Santee_Native

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ka0tyk

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Santee_Native

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Kyle700

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FSMMARINE

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mobboss

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renegade

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Wayne Zighter

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IRRebel

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Santee_Native

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mash on it

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SLCKREG

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