429 backfiring at idle

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Oct 12, 2007 | 06:54 PM

evam350

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429 backfiring at idle

Hi everyone

I have a 73 F100 with a 429 and it was bogging and then backfiring when I would stomp on it. I changed the spark plugs and rebuilt the carb and now that problem seems to have gone away but it doesn't want to idle very good and backfires alot

Anybody have any idea what would cause backfiring while the truck is just sitting and idling??? Could timing have anything to do with it??

I checked the to make sure I didn't get any plug wires crossed and they all look good

also its a 4300 carb and it doesn't have points (it was converted to duraspark)

Thanks for any help

Oct 12, 2007 | 07:48 PM

truckerpups

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Sure sounds like timming to me.

Oct 12, 2007 | 07:49 PM

evam350

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Do you think its too advanced or too retarded??

Oct 12, 2007 | 08:35 PM

evam350

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Forgot to mention in first post it is backfiring out the exhaust, not the carb

Oct 13, 2007 | 06:59 AM

trinogt

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From: Eustis FL

Check the timing, then maybe find a friend with an Edelbrock carb you can borrow and bolt it on to test. Might have a plugged jet from accelerator pump, especially when you say you step on it when it happens.

Oct 13, 2007 | 11:47 AM

evam350

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Trino it used to bog down and backfire when I would stomp on it but that seems to be better now it backfires while its just sitting there idling

I have an Edelbrock 600 on my trans am and the cars gonna be off the road for awhile so I was thinking about just bolting it up on the truck and see if it makes any difference

Thanks

Oct 13, 2007 | 05:03 PM

trinogt

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Joined: Apr 2001

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From: Eustis FL

That's a perfect idea... I run a 600 Edelbrock currently on my 460... I know, it's small, but I have it tuned just great. It ran well even before the tune, but rich.

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Oct 13, 2007 | 08:44 PM

bronco521

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From: right here in michigan

bad valves,hammered out exhaust seat.compression check will let you know if these are a possibility.i had a valve seat go bad on my old 429 and it did this.

Oct 15, 2007 | 06:04 PM

#10

evam350

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Compression check shows 120 psi or a little better in all cylinders except one which has 150????

Also 2 of the spark plugs were blacker than the others, does this indicate anything??

Oct 15, 2007 | 11:55 PM

#11

Mil1ion

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Joined: Jan 2008

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Black soot is from a Rich Mixture.

Let me guess ...cylinders 4 & 8 ?

Oct 16, 2007 | 03:56 PM

#12

trinogt

Cargo Master

Joined: Apr 2001

Posts: 2,364

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From: Eustis FL

Try a little shot of oil in each cylinder and test compression again. If it stays the same, it may be time to rebuild the heads. If compression comes up, then the compression ring on the piston is likely worn.