I have a strange problem with my ST 40. When the the fuel tank gets down to 1/4 the engine causes foaming of fuel and dies. This only happens at full throttle. I left everything the same including prop and spinner put in well used OS 40 Sf, no problem runs the tank dry. Any idea what it could be? Anything I can look for? Problem has been since the motor was new.
Thanks

FB,
There's a few things i would think of:

1) check for an out-of-round crank that is causing vibration which is foaming the fuel;
2) check the tuning of the engine. If it is getting hot enough, it will vaporize fuel in the line and may look like foaming fuel.
3) Look for a problem in the engine mounting, including a cracked crankcase that is allowing the vibration.

If you're not able to find the problem there, send it for service.

I must congrulate Super Tigre they replaced the crankshaft under warranty. Even though I had the motor for more then two years (hardly used though).

Thanks!!!!!