I do not recommend using a pair 450 Holley on a small engine. It will spit back or will back fire. The plug will load up, too. The 450 Holley are set up for large cam where manifold vacuum is very low. and High compression piston. The secondary are mechincal, resulting boging if you hit the gas pedal hard. Your better off using a pair of Holley 390CFM. It will give you a total of 780CFM combine. They were made the street. The secondary are Vacuum. They will adjust for the engine needs.