I have an -10-12 year old XT85T Poulan/Weedeater that does the same thing. When I first start it it runs a couple of minutes normal then begins to stall, then I start and run it with the choke half way out until it starts to stall...then as it staggers along starving for gas, I push the primer bulb to keep it running. I've cleaned the air filter, the spark plug, the exhaust port, put new gas in...all unsuccessful. I was going to replace the fuel filter (fuel pick-up assembly), but it looks like you already tried that. If you get an answer, I'd be interested...it may be my problem too. I suspect the carburator needs to be rebuilt.
Ralph
August 2008