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!

Skip Burney

how did you set them when you built the engine

my 76 ray

Check your firing order.

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.

southern_vette

or i could be just a timing issue

Lon Wayne

Spark plug wiring?????

Easy Mike

Could be. Could also be timing.

Copacetic

I adjusted the intake valves when the exhaust was just starting to close and I adjusted the exhaust when the intake was opening. I brought it to zero lash and tightened it a little more than 1/4 turn of preload.

I checked it again, all the wires are hooked up right.

I have it set at 8 deg BTC @ 800 rpm. total timing somewhere around 32 deg.

jn76vette

My new engine had the similar symptoms with under twenty miles. It had the exhaust lobes for 7 & 8 rounded off. Hopefully that isn't your issue, but it might not be a bad idea to check the oil for metal.

Copacetic

I went ahead and readjusted the valves. Took em to zero lash and gave em all 1/4 turn of preload. I just discovered I'm getting misfires on some cylinders. I'm also getting a little knock. I now am leaning toward a leaky intake manifold. Ill test the manifold vacuum and get back to you.

Skip Burney

Sounds like it might be going lean for some reason, the knock would scare me though

Copacetic

Vacuum gauge bounces between 4-6 at an idle. And it slowly rises up to 20 when i increase the rpm. It only gets to 20 when its revving around 2500. I cant figure out what that means.

Easy Mike

That's what the book says, but that extra 1/4 turn might be too much. You might want to consider backing them off a 1/4 and trying that setting. My 68 327 did not like the extra 1/4 turn.