Honda Engines GX390 Parts Lookup by Model wwwssmallengines››Honda Engines›Engine›GxEnter your Honda Engines model number below. Click the Search Button to See More Results. Parts lookup for Honda Engines power equipment is simpler than ever. Enter your model number in the search box above or just choose from the list below. Honda GX390 Engine Parts - Honda Lawn Mower Parts Honda GX390 13HP Engine Parts Honda GX390 13hp Engine Parts Diagrams Honda's GX390 13 HP engine is the largest single cylinder OHV engine that Honda builds. It boasts a small foot print for easy mounting and can power applications that pose difficulty in mounting a twin cylinder engine. The GX 390 is quiet, smooth and vibration free.