I'm working on a customer's 1968 mustang with a 302 roller engine in it. It's got Ford racing heads, a single plane intake, new Holley 600 carburetor, new Mallory distributor and protector, new resistor, new coil, new ngk plugs gapped to .042". I can get it running and it runs alright but eventually stalls and won't start again for a few minutes. When it revs to about 4000rpm it backfires through the carb. I'm getting between 110 and 135psi on a compression check with every cylinder being different. After a while it starts smoking as well but not a ton. Hot compression is the same as cold compression, I also tested functionality of the gauge to verify it. It keeps carbon fouling the plugs pretty quickly as well. Any thoughts on this would be great. Thank you.