So we need to start looking to isolate the problem ( s) .
Easy start is a can of carb cleaner
Remove on plug spray a very small amount down the plug hole put the plug back & crank the engine
It should go bang once
Do the same with the other side
If no bang, do it a couple of times more just to be sure.
If both sides went bang, pull off the air filter and spray some down the carb throat
Should go bang a couple of times.
If so then try again & just before the engine dies give it another short shot,
If you can keep on doing this for 1/2 a minute or more then your problem is in the fuel delivery system and the timing, coils & valves are OK
Get back with the results so we can take it further.