Chainsaw Repair

OK, so i bought my son a champ for x-mas . I knew it needed some repair , no big deal I've done it all on saws ... I thought . Anyway after getting it cleaned up , it needed a fuel filter and a carb kit. Got that done and fired it up . Realized why they called it a champ , the thing ran super and cut great .... for a while then died . But it would start right back up and die . So I refilled the tank and it started and ran great again ... for a while . Same thing. I figured the fuel line was cr acked where it goes through the tank , and replaced it . It wasn't bad . So I fired it up again and it was fine ... until my son used it for a bit and the same thing happened. I told him to switch the position of the impulse line and the one to the carb thinking I'd switched them . Anyway that wasn't the problem either , but the thing runs great if the tank is full . Use it a bit , and it will die . What am I missing ?

Could be the tank vent, doesn}t really run long enough to get coil hot

Thanx , I'm gonna check today

If you're bringing an old saw back to life for use as a work saw you should replace the crank seals.  Like the fuel line and carb diaphragms, the crank seals are rubber parts with a finite lifespan.  Sometimes crank seals will leak (or leak more) when hot.  When they leak, the impulse signal to the carb gets weak.   That will cause the saw to lean out.   A weak impulse signal afects the ability of the pump section of the carb to consistantly pump fuel from the the tank to the metering sectiion of the carb.

People often 'tune out' an air leak by richening the carb settings (often without even knowing that they are compensating for an air leak).  This can work for a while (until the leak worsens), but is bad practice and will eventually lead to damage.

Contrary to popular belief, a 2 stroke engine often does not 'race' or refuse to slow to idle speed when it has an air leak.  Those symptoms do happen sometimes, but not always.  Same goes with changing tune/idle speed with tilt.  That is a good indicator of a leaking crank seal.......but it does not always happen when a seal leaks...

Just bought a doz from Jacks.  They were actually cheaper than AM's from Northwood.  I change them all the time too.
Shep