I'm no mechanic, but I'll check these things out. The gas is new, plugs were changed the beginning of this season, the tank is being vented. I normally just use the choke to start it when cold. The tank is an old 6 gallon steel one. There's no vent screw on cap, I was told to just crack the cap open slightly to vent it. So the problem must be something with the tank, dirt in fuel system, or fuel pump? How do I check the primer bulb? Thanks.