GX390 : What size carb / brand should I use?


New member
Currently building A Loncin GX390 Modified engine and aiming to get 40 horsepower out of the engine as well as reach a maximum rpm of 8000. This is not for any competition and such any carburettor allowed. What would be my best choice of carburettor for my engine? Using a 40mm Inlet valve and 35mm exhaust valve.

Was told to use 33mm Mikuni Pumper Carb or 34mm Flatside normal Mikuni carb, but wouldn't 40mm pumper flatside Mikuni carburettor be the best of both worlds?

This engine will be used on sprint kart tracks around the UK such as shenington and whilton mill if that helps.
Based on the specifacations you offered, the Mikuni 33 carb would be more than adequate. I don't see an advantage in using the Mikuni 40 unless you have head flow numbers to post.