The first thing you need to do is check compression and fire..ignition..then take a fuel sample checking for water. if these things have been done and all seems ok then try running on a seperate fuel tank and line..this will help determine if the issue is on the engines fuel components or that the tank and line system are faulty. with the ignition system on this engine you could be losing spark as you try to gain rpms based on the high speed and low speed of the ignition system which can occur between 1800 and 2200 rpms. also does the engine cut completely off or does it just seem to bog down. good luck