Once it is cool it will start but after running under load about 20 minutes it starts to choke out like it is running out of gas - I have changed the fuel, fuel filter, ran with the cap off, blew through the vent tubing, sprayed carb cleaner in the carb, cleaned the top of the engine - nothing works - any ideas?

I am having the same issue. I have rebuilt the carb and done what you have as well. Does anyone know if this could be the fuel pump?

I gave in and took my John Dear LT160 to the dealer - he replaced the carburator.

He said the flow tubes are so small that it is nearly impossible to rebuild the units.

So far so good - it now runs fine