This is a guessing game without more info, but presume fuel is getting to the carb, your wires/spark is good and timing events from the distributor are as they should be. Do you have PTFE fuel hose forward of the pump? Slight cracks (even on the return side) will do that. Also pull the valve covers and inspect just in case.
I've also seen internal detonation cause this issue (hope not!), but if you don't find the issue do a quick compression check. Fingers crossed it's something simple Bro
