buy a cheap in line spark plug tester & a can of starer fluid.
Hook up the plug tester and watch to see if the flashing tube stops flashing before the engine stops.
If it does not stop flashing till the engine is almost stopped then you have a fuel system problem.
If it stops flashing with the engine running at full throttle then you have an ignition problem.
So for $ 5 you have halved the work in diagnosing the problem.
If it keeps flashing while the engine is slowing down spray a little starter fluid into the carby, NOTE I SAID A LITTLE and for safety sake from full arms reach, just in case it backfires.
If you can keep the engine running with little short burst of starter fluid then it is not getting enough fuel so the prime suspect will be the fuel line, tap ( if fitted ) , filter & pump as you have just put on a new carb.
