Husqvarna 55 Chainsaw (1999) - Runs OK for 1 minute then stalls

I have a 1999 Husqvarna Chainsaw (Model 55) that's been having trouble running lately. I finely got it working OK this weekend, but after about 1 hour of use, it died and I was unable to get it running again. So, I dissassembled the carburetor and soaked the parts overnight in Gunk Carb Cleaner--I removed everything but the plugs before soaking. I just put in a new fuel filter in the tank and new air filter. I also checked the ignition coil (appears to generate a nice spark) as well as the muffler and spark arrestor. I also checked the tank vent... it was not plugged and I was able to blow compressed air through it in both directions. I have not changed the spark plug yet, but I did clean it.

Now, since I cleaned the carb, I was able to get it tuned to run great, but it only runs for a minute then stalls out as if the tank is vacuum locked. As the engine starts to run rough, I open the fuel cap and it revs back up and runs OK.

Could it be the tank vent even though I'm able to push air through it? Could it be the fuel pump on the carburetor? Could there be some passage ways in the carb that the soaking can not clean out? Also, this saw does not get used much and sits most of the time with fuel in it--this is why I suspected varnish build up in the carb.

I was going to try a new fuel tank vent next. Any suggestions out there?

Thanks!