Changed the entire carb.
I have loosened the fuel cap and even removed it - same problem
Carb p/n 640330
What is the fuel quality where you are at? Is the fuel less than 3 weeks old? Have you tried swapping out the ignition coil to see if it's failing?
I figured it out. After the engine quit at full throttle II snatched the float bowl off. It was almost dry.. Turned float bowl upside down to check for float and needle/seat for movement. Hardly any travel (way less than it should have been). Moved float up and down while blowing thru inlet, very little to no air coming thru needle seat regardless of float position. Float is a 1 piece arrangement with no adjustments. I tried to bend/adjust in float attach area and 2 of the little struts broke, but the main attach struts remained intact. Turned float bowl upside down again and had normal float travel and air would start and stop when blowing thru the inlet. Re-installed float bowl and fired her up. Worked great under all load conditions. Don't know if this was a manufacturing defect, or the float deformed over time, or the needle seat shifted upward over time.
NOTE: When installing the jet pipe in the bore of the float bowl I found it works the best when you push it most of the way down the bore (not all the way) and having the holes in the jet pipe facing the shut off solenoid.