I have been messing with a 40cc Briggs 4-stroke. I installed a CRRC ignition. By messing with the timing and the pop off lever I have a decent running engine. I am getting about 15 lbs static thrust, mid 5500rpms with various 20-22" props. The carb is a WYL142A/ 504. I don't see any refrences to it on the Walbro site. It has a 9mm venturi. I feel the itch to get a WYK carb, those have ajustments.

I have had no luck with getting a butterfly type to work properly despite various tricks to make them work. So I guess I need stick to the barrel type. Should I stick with the 9mm or go a little larger?