[zellerj]

Sometimes the inner portion of the exhaust hose collapses and closes off the hose, but it looks perfectly fine on the outside. To check for this, some people attempt to start the engine with the exhaust hose disconnected. Messy, but it points you to the right direction if starts with no exhaust back pressure. Typically with a collapsed exhaust hose it will run better in neutral than under load.

Have you tried starting the engine with a short squirt of starting fluid into the intake of the carb? Be careful that you have good ventilation when you do this, because ether is much more explosive than gas. If it starts with starting fluid then the issue is carb or fuel delivery related.

I bought a new carb from Moyer when I was having issues. It was cheap when one considers how much time is spent tracking down a carb issue. If you go the new carb route, make sure the gas delivery system is pristine, no water in tank and new polish filters, or you will have the same issue down the road.