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BBC backfiring when warmed up issuse

653 Views 6 Replies 4 Participants Last post by  cbreezer
Ive got a friend(with no computer) who just picked up a drag boat and the guy he bought it from couldnt tell him much about the motor except that its a BBC, solid cam,dual holleys. When the engines cold it runs and sounds great but once it warms up it starts backfiring, if you let if cool off and restart it it'll still backfire unless you readjust the valves, he did take it to a shop and spent about 1500.00 on it and it still runs the same.
I was hoping maybe you guys have come across this or might have an idea he hasnt checked out yet.

Thanks, Tom
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What did he have done at the shop?

Could the engine have been built for the use of higher octane fuel?
I'll find out tomorrow what he had done at the shop and what octane hes running in it.

Thanks, Tom

Since he knows nothing about the engine, start with the basic's.

First do a compression test.

Second check the ignition system, cap rotor, wires, and install a brand new set of spark plugs.

Then it's off to the fuel system.

As a side story, don't put alot of faith into the shop before you working on it. I have a friend who bought a truck off of me about a year ago. A few months back it started to have a mis. He took it to the local garage and they charged him $600 to replace the head gaskets. Well last week he called me and it was doing the same thing again. I looked at it Saturday and all it needed was a cap and rotor, problem solved.

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Found out alittle bit more today about the motor, its a 427 and when he had it worked on last the guy resurfaced the heads and put new valve(dual) springs on it.Hes running a Mallery ignition system on it and hes tellin me hes running super in it and it has 11/1 pistons(which are domed) which to me sounds like more than 11/1. It is running a roller rocker setup on it and he did tell me that the last time he ran it, it ran great till in warmed up then started backfiring and once it cooled off they checked the valves and all the adjustments where good and it ran great once again till it warmed up, he hasnt done a compression test on it yet.Im wondering if maybe he having a vacumn leak issue.

Was this boat purchased locally, if not from where? Altitude, different climates, and Holleys don't mix.
How about checking the valve lash when the problem occurs?..Ron
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