Os 1.20
 

I havent heard of any problems with them. Does the pump have a regulator? On pumped engines, you need to have a REALLY good fuel tank. That can be a severe problem, and thats the only time I've seen them quit. The YS engines are really bad about it. I've seen a few of them blow the seams on the tank before. They have a pressure pump though, and I'm not sure what type of pump the OS has. When I say this, I mean does it suck fuel to the engine, or pressurize the fuel tank.