Pop in rebuilt 454
 

I have twin 454's in an early 36' Sonic (1984). They were run-out so I had them rebuilt a few weeks ago. While they run great now, I still have the same "pop" (backfire) in one of them that I had prior to rebuild. It occurs above say 3500 rpm; a single pop that may occur now and then again in 5 minutes sometime sooner sometimes later but if it's running over 3500 rpm, it's going to pop. I've swapped carbs, coils, thundberbolt IV packs. I've had 3 sets of ignition wire, plugs and distributor caps on it. Heads were replaced (old ones cracked) with new valves, seats, guides, springs. Running solid lifts & cam. Still have the pop in that engine. Appears to be through the carb to me. Will try swapping the Distributor itself this weekend. Out of ideas, any help would be greatly appreciated at this point.

You may want to post this in the Tech area if you have not already. I wonder if they set the valves a little tight?

Jon

Thanks Jon, I'll post it on tech forum, I'm new to this.

I had teh mechanicas run with me and they seemed to agree that it was in ignition. They are not really comfortable as they only do re-builds and seldom ever get into the running after the rebuild unless they have a problem. Sounds crazy but that's the shop they run, you bring them, they rebuild them. Based on what they found (especially with this particular engine) I was happy they did the work.

It's just strange that it has the exact same pop after being totally rebuild. I check those valve. Thanks.

Al

I JUST HAD THE SAME PROBLEM
I REBUILT MY 2 NEW MOTORS, BROKE THEM IN AS SOON AS I PUT THE THROTTLE TO THEM AT 3500 RPMS
THE ONE MOTOR STARTED POP POP POP POP
CHECKED IGNITION COULDNT FIND ANYTHING WRONG SO I PULLED THE MOTOR TOOK THE CAM OUT
AND HAD LOST A LOBE ON A CAM 3 HOURS OLD

I had run a lobe off of a previous cam a year or so ago within two hours of buying the boat, but that one popped all the time once the lube was gone. This pop happens every now and then, minutes apart and it was there before the rebuild and is still there since the first few minutes on the fresh engine. Will keep that in mind though. Thanks for the response.

Al

Cams were changed. Had them install new cams & lifters as they found two different cams in the two engines and I didn't want to fool around. So, new solid cams, lifters & springs from CompCam for both engines. Thanks for the resposne.

Al

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