This carburetor started life as a standard Genuine Honda GX390 carburetor with a 21.5mm bore which has been machined on our milling machine to 23.5mm and then finished by hand porting & polishing for a perfect finish with a final 24mm bore size which dramatically increases its airflow, combined with its reworked fuel circuitry this carburetor is ideal for open engines and can help to achieve over 20HP!