350 backfiring from carb, stalls under load

[BabyBlueChevrolet]

1973 Chevy C20 with 350. I just redid the intake manifold gaskets and it fired right up, idles good, but when i put it in gear and give it gas it just backfires and dies. I’ve messed with the timing, advancing and retarding but it doesnt seem to help. I have relatively new carburetor (demon 650), new HEI distributor, wires, plugs. It idles good but just dogs out when i give it gas. I can even rev it just fine when its in neutral. Any help would be appreciated.

 

[Radiohead]

Lean mixture from the squirters not squirting?

 

[Craig Nedrow]

What Eric said...Backfiring through the carb can be caused by several things, but in this instance, probably a lean condition caused by a leak. You said you messed with timing...backfiring through the carb could also mean your intake valve is still open when it fires on the power stroke, blowing through the carb, so would need to be retarded.

 

[fast 99]

Has vacuum been checked? Broken valve spring or other valve train issue?

Doubt it is root of the problem, Demon carbs do not belong on SB trucks. Can't for the life of me understand why that choice. They are tractors that need torque.

 

[Copakekid]

I know you have a different carb, but I had that problem with my 73 Javelin and a Holley Carb. I put an edelbrock intake and carb on it and still had the problem.

Turned out the intake wasn't milled square and I had a huge vacuum leak. Ended up putting the adapter plate on it to get it to seal. After that it runs fine.