Hi Norm,
I guess you would have already checked that the flywheel key wasn't broken ,sometimes the flywheel is a
little loose on the key when you go to install the flywheel so I like to turn the flywheel to the most non advanced
timing position as possible then tighten the flywheel nut. The other way to do this is to grind down the thickness
of the key a little so you have movement or even remove the key completely and change the timing and see if
you get no kick back when starting and running then make the key fit in the best position that the motor works.
If you had an old spare flywheel you could file the keyway out to get less advanced timing ,but not worth
damaging the original flywheel if this doesn't work.
If it was a timing issue you could mark top dead centre on the flywheel and motor with white paint and
check with a timing light with the engine running or check with the timing light with the plug out and the
drill to turn the motor over.
I've seen a few motors back fire from a faulty spark plug or a faulty coil.
My neighbor has a 52cc line trimmer and he broke the flywheel so I gave him another flywheel and he broke that one too,
it turned out the starter would jam up when running ,so I then gave him another starter but had no
more flywheels that size. A lot of these Chinese parts are poorly made .
Cheers
Max.
