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.
Thanks Bax, it's good info, I have a G2300 that I converted to a Walbro carb, I used 12:1 gasoline/oil ratio for break in and 16:1 thereafter, I removed the backplate yesterday to have a look inside, it looks 'like new' but obviously petrol mixes need less oil.
The conrod is beefy in design and the crankpin is wider than most other engines with similar capacities, I think it will take a lot of abuse before giving up. I know it was not designed to be used with gasoline but 'fiddling' is part of the hobby and anyway it is no longer under warranty. Do you have a view on oil contents with gasoline?