Copacetic

The problem im having here is im getting a backfire through the front drivers side barrel of my carb. It doesnt happen at an idle but just when i give it a little gas then poof and the engine dies. I was running a 600 cfm edelbrock then i tried a 750 and that had the same problem and it was too big of a carb anyways. So today i put the 600 back on. So could maybe a valve adjustment be off and thats what is causing the backfire?

Its a newly rebuilt engine so i know its not a rubbed off lobe or a fowled up valve. everything is new with less than 30 miles on it.

Thanks in advance!

73, Dark Blue 454

Backfiring through the carb? Yes, could be an incorrect valve adjustment. Or broken valve spring. Could also be firing order problem or a timing issue. And yes, a wiped lobe(s) will cause backfiring through the carb.

Better describe the problem. Does she idle nice and smooth. Does the backfiring occur under a load or randomly during cruise?

jackson

New motor is more likely to wipe a lobe than an old, well broken-in motor.

Popping back thru carb on a new motor is likely caused by lifters/valves adjusted too tight.

Copacetic

The pop happens 90% of the time under a load. When i first take off in first gear. And it happens in the top end of 3rd and 4th gear typically around 3000 to 4500 rpm It has happened a few times with the car in neutral and right when i give it a little gas. But normally it idles nice and smooth and acts just right in neutral just sitting there.

Ive checked the firing order again and all is in order. New plugs new wires clean contacts in the dist. I have the timing set at 8 deg BTC @ 800 rpm. Vacuum lines on the carb are plugged and the vacuum advance is hooked up correctly.

knodty

Not sure if you have a big cam or not but i would put your base timing up a little to say 12-14 deg as my BB would pop out the carb intermittantly until i put more initial timing on the crank at idle, but this only happened on take off, so your problem sounds more like a sticking valve or incorrect lash adj.
Good luck

73, Dark Blue 454

Agree,..set your timing to give you 34-36% degrees mechanical at 3000 RPM (vacuum advance disconnected).

Let the initial timing fall where it falls.

See if that smooths her out.

Also, you sure the distr. cap is good? Not cracked?

Copacetic

I set the timing to 35 deg @3000 rpm. I took it for a little drive and it didnt backfire. Yeah its a new cap so no cracks.

But its for sure not firing on all cylinders. I dunno what could be wrong there. I am getting spark, I checked that. The wires and plugs are new. I was letting it warm up before i readjusted the timing and while it was warming up it seemed like it would fire on all 8 for a sec then not. down to like 5 to 6 cylinders at a time i think.

whitehause

The spark plugs should tell you which aren't firing. The plugs could just be fouled from the previous problems. I would also re-check your valve lash. I never go the full 3/4 turn after zero lash that they suggest.(assuming hydro lifters) If you did, maybe back the nuts off 1/4 turn or so.

Copacetic

I think the issue was that the timing was off and 3 bad spark plugs. Its running very well now.
Thanks for the help guys.