To answer Prigal, the G20/2300 will be destroyed if you a low-oil fuel, so I likely meant to say "clearances" and not "tolerances" above. The S-2000, S-2500, S-3000, G-3250, and G-4500 need to be run on fuel that's 12%-15% oil until they are well broken-in, and then fuel with an oil content of 10%-12% can be used. SuperTigre recommended that the oil be 100% castor oil in all cases. That's how they designed the engines.