popping at high rpm

I'll guess something bent/broken in valvetrain.

Any of the plug gaps closed up?

5/16 line can feed that OK, a 3/8 line would be better. Suck air through a 5/16 line and then do the same with a 3/8 or 1/2 line. The mechanical fuel pump does the same.

As a baseline, try to jet change 2 sizes at a time. Only time I would go more is if I had an air/Fuel meter that displayed a really rich/lean condition.