Bad Plug?
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Elder User
Joined: Jan 2005
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From: Silverdale, WA.
Bad Plug?
Finally got my 77 with the 71 429 motor ready to fire today, fresh gas, new autolite 45 plugs gapped to .044, wires all checked good, new cap and rotor, fresh fluids, etc. When I fire it for the first time it makes this horrible pop/backfire sound out the pipes fairly consistently. Shut it down, rechecked plug wires and firing order and all was right. Fired it again, all the same still. Pulled plugs, they are dark and sooty, so I know I am running pretty rich, but #4 plug was oily on one side and just clean porcelain on the other side, didn't look to be firing. It got too late to keep tinkering tonight, so I am trying to ask if this sounds like a bad plug, or should I be looking somewhere else? I did do a compression test on all cylinders, they all cranked 165 +/- 10 so I don't think that I have a stuck valve. Suggestions are welcome, my best guess is a defective plug...
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Put the plug in a different hole and if you still have a problem, then change it. Why gapped at .044? I would think .035 would work better. You could have a carb running way rich and/or the choke to tight. Next time you start it, manually open the choke shutter valve and see if that helps.
PS: Geez, you're in my backyard almost.
PS: Geez, you're in my backyard almost.
Elder User
Joined: Mar 2004
Posts: 976
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From: clinton iowa
i had similar problems with my 429 when i got it running ,all carb related only my carb had some serious issues that we couldnt resolve, so i bought a new one (750 holley ) and no more popping.has yours been rebuilt? should"nt have any gas problems with 165 compression .did a compression check on mine and its doing 195 .good luck 
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Elder User
Joined: Jan 2005
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From: Silverdale, WA.
Wow, two replys and I could almost walk to your door from where I live... I know long walk, but better than say, florida...
carb is manual choke, so I know the choke was open. Carb was rebuilt not too long ago, guess I will have to do it again...
I'll try switching plugs and see if that helps, I've been looking for an excuse to go to a Edelbrock EPS800 anyway.
As for the gap, I thought all 429/460's with the electronic breakerless (non points) ignitions were gapped to .044, maybe this is the problem... Distributor is D8TE, using standard ford ignition module.
carb is manual choke, so I know the choke was open. Carb was rebuilt not too long ago, guess I will have to do it again...
I'll try switching plugs and see if that helps, I've been looking for an excuse to go to a Edelbrock EPS800 anyway.
As for the gap, I thought all 429/460's with the electronic breakerless (non points) ignitions were gapped to .044, maybe this is the problem... Distributor is D8TE, using standard ford ignition module.
Last edited by hotrod_ta; May 22, 2005 at 11:43 AM.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
If the carb is a Holley, all it takes is one little backfire and the power valve is blown, unless you have a power valve protector installed. As to the gap of the plugs, the electronic system still uses a standard coil and I would suspect .035 would be better.
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Elder User
Joined: Jan 2005
Posts: 726
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From: Silverdale, WA.
Carb was a holley, now it is on the bench. After changing plugs, it would fire and run o.k. at 1500-2000 rpm, everytime I went back down toward idle it would start popping and backfiring out the exhaust.
So... anybody have a 750 cfm edelbrock with a manual choke for cheap?
So... anybody have a 750 cfm edelbrock with a manual choke for cheap?
