1973 Rebuilt 460 with a one cylinder backfire

Thanks in advance for any help. I built a 460 with 10:1 compression, MSD box, mild cam, headers, magnetic dist., and a 750 carb. I have a series of small backfires confirmed from cylinder 4 (passenger's rear-most). I
swapped out the plug, changed the wire and cap, readjusted the valves, triple checked the firing order, it runs great accept for the backfire. Do I have a valve problem? Thanks
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On Mon, 22 Aug 2005 12:07:50 -0400, "frankpalumbo"

What you describe is classic of a valve train problem like a bent pushrod, a weak valve spring, a sticky valve or a flat cam lobe - well, it isn't really "flat". It may have gotten the nose knocked down a bit if the breakin wasn't done the way it should have been. It only takes a few thousandths to really screw it up. Did you follow the cam grinders instructions on cam lube and breakin procedure? Also, if you are using points for a trigger, a bad or shorted condenser will do that.
Lugnut
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Thanks Lugnut. I definitely had the cam well lubed and did not drop or force it into place. I pre-lubed the lifters before installation and the engine before starting, and ran it up real easy. Not to say I still dont have a jocked cam, but your note confirms my feelings that I have to chase the valve train, starting with the push rod. Thanks again - FP
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frankpalumbo wrote:

What does a compression and leak down test show on that hole? No leaks on the intake?
Bob
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don't suppose you are getting crossfire from another wire?
--
Dave MacLeod
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dmac wrote:

Aaah, you might be on to something there. I recall being told on most older Ford V-8s to always have the wires to cylinders 7 and 8 cross each other because they were inline in the firing order and the long run to the cylinders could cause inductive coupling between the 2 if they were side by side for the entire run. That is a long forgotten tech tip from my youth. The problem does sound like a worn lobe on the cam though. For breakin, I was taught to initially start the motor and run it at ~1800 rpm for 20 minutes to break in the cam. The big thing was to get it above idle for full oiling and to maintain steady speed for this time to minimize wear.
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Thanks Tom
I'll check it out. I currently have the head off and will be looking into the condition of the CAM.
FP
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