mine has a large (22mm, or bigger I think even) mikuni carb and a 90cc bore kit I was told. it went in like 2 hours max. but I think it was less, like around 1hr.. I thought to do a plug check, u stall it at wot full speed? I may do it but it runs ok to me for the most part. I looked at the plug and it is black and a little gas wet sometimes but I gotta measure my carb and such to know what it is before I go buying jets. thinking about trying a hotter plug we'll see.. I have a digital caliper so I can measure the carb, just been lazy. I'll do a plug test maybe on the next ride. but I need to clean the filter 1st and the plug to a new one as that's how you're supposed to do it.. then do the test. but it's got a pipe and is loud so I don't ride it around the neighborhood so I'll have to do it on one of our riding sessions, just take a spare new plug, put it in, stall it at full speed wide open throttle and pull the plug and let the kid ride w/old plug can also try adjusting the needle setting as we don't usually run under 1/4 or full so that's basically in the needles range, where we do majority of our riding... alot of people don't seem to understand that and jump straight to adjusting jets... needle controls a/f between 1/4 and 3/4 throttle not just the main jet.