An internal combustion engine having a crankcase, a cylinder connected to the crankcase, a compressed air assisted fuel injection system connected between the crankcase and the cylinder, and a reciprocating piston head located in the cylinder. The improvement comprises a fuel delivery system having two carburetors that switch delivery of fuel to two different locations based upon the speed of the engine. The system uses an accumulator with piston ported reflected compression wave delivery of scavenged compressed air to deliver fuel at a wide open throttle position.