Hi there

paul 46 here.

all being well and compression and spark and timming , muffler is clear , carby is clean , and diaphrams are all ok , fresh mix , and fuel filter and lines are good

does the unit run with 2 stroke mix in the plug hole - ?
if yes assume compression and spark are ok,, if no check compression and spark and muffler

will the unit run with 2 stroke mix sprayed into the carby throat ?

if it does sounds like you have a air leak somewhere in the intake system

could be at barrel base gasket, c/case joint, manifold boot/ block gasket, carby gasket , impulse hose ,if this unit has one , c/case main seals leaking

2 strokes need air tight c/cases in order to pump fuel / air / oil mixture from c/case to cylinder
and to create a vacuum for entry of fuel/ air / oil mix from carb to c/case

symptoms of air leak are -: hard to start, wont idle, stalling, low power, inconsistant idle, over rev
overheat

pressure and vacuum testing can be done by blocking off intake and exhaust with rubber and metal plates , then fitting adapter to spark plug hole , and placing piston at bdc , pressureise cylinder to 7 to 8 psi of pressure and check areas , base gasket, manifold joint, main seals, , impulse hose ? for leaks with soapy water - if leaking bubbles will be evident

if no leaks and pressure is held at 7 psi for at least 2 minutes with dropping - presure test is good
next do the same test using vaccuum again go to 20 - 30 inch / vaccuum

if vaccuum held unit is ok

suggest take a good look at carby particularly if P and V test are good and spark coil tests good with a coil load test using a spark gap of 6.00 mm to stress the coil ( simulates spark under compression load)

have a look and let me know what you find

cheers pauly46