Or some more pieces stuck in the top of the piston hitting the head-do yu have alum or iron heads-what type intake manifold? If a 180* type pices will go back and forth into all 4 clyinders of the 180deal
2 end cyl on one side, 2 center cyl on other side-------3,5 and 2,8

was throttle linkage or return spring bracket fastened to carb with that stud?