Small Engines (Lawn Mowers, etc.): Weed Eater Blower, gas cap, leaf blower

Question
I have a Weed Eater Feather Lite 1500 19 cc leaf blower with a Walbro 214WT557 carburetor. It runs fine for a few minutes then surges like it's running out of gas. When I loosen the gas cap, it runs fine again for a short while, so I think the problem has something to do with venting. When I look at the primer bulb, I see lots of air and gas circulating in it, but none in the return line. The lines are all clear, and the carburetor seems to be clear throughout.
My question is two fold: Is the gas cap itself supposed to be vented? This one looks like it should be, but I cannot blow any air through it.
Secondly, is there something in the carburetor that should be supplying air back to the fuel tank, and if so should I be putting in a carburetor kit?

Thanks

Mike

Answer
Yes the cap should be vented. It's kind of a one way vent though so in can be used in various position with a slight turn and not leak. If your blowing into the cap from the tank side you won't be able to, or should not be able to blow out of the cap, it just lets air into the cap....Tom