My son's 90cc sportman hasn't been running well all last year. he could sometimes ride for a few minutes with out problems but most of the time the RPM's wouldn't get high engough to engage the clutch. the throtel would only silghtly rev the engien above, idel even wide open. We put it away for the winter. This spring we pulled it out and now it will only start and run for 15 seconds if the throttle is wide open. after 15 seconds it stalls and wont start again until a few hours later, where it again only runs for 15 seconds.

Here's what I've done so far
New battery
New Fuel
Carb cleaned and all jets and passages clear
New spark plug(same type that was in there)
No leaks around intake
compresion check 45 psi (I replaced cylinder, piston , rings,)now have 115psi

Im now thinking I might have bad crank seals, but I would like the forums ideas before I tear into this thing again. Thanks -Duncan

 

Here is a manual
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The stator commonly fails on these and can cause intermmitant spark. Follow test procedure in the manual.

Also I'm wondering if the exhaust could be plugged with all that 2 stroke oil, though that should not cause it to stall.
I believe this stator will fit it if you reuse the grease seal out of your. it is the same as the polaris one other then the seal which is easy to pop out and reuse and 1/2 the price

Stator Magneto 29 for 2 Stroke Engines 7 Coil - Sm272-29 - 2-Stroke Stators - Stator Magnetos