What is the oil content of your fuel. An engine that runs only for a few minutes and quits indicates it's getting too hot.

O.S. states that the oil content should be no less than 18% by volume.

Also check the idle mixture. Many times it's too lean. Richen it a LOT and work with the high-speed needle first. Then go back and get the idle mixture adjusted once you have the high-speed sorted out.

If all else fails, put the engine on a test stand and see if you can get it running well. If it runs well on the test stand and not in the model, then the problem isn't the engine, but the combination of the model, the engine, and the fuel system.

If it can't be made to work even on a test stand, it should be sent to the service center.