Big Red atc250es big bore kits ????
 

I have a 1985 atc250es big red I was looking trying to find out information about the cyclinders will or can you interchange or buy a bigger bore cyclinders I can't seem to find anything at all looking at some pictures I was wondering if any 300's would interchange or if I could buy a big bore kit haven't found one yet seems like someone would sell one

The 250 and 300 have the same bore, so fitting the 300 cylinder wouldn't up the capacity, even if it will fit. It is possible the complete engine may fit, but there are quite a few unexpected differences, the 250 is AC ignition, the 300 is the strange AC/DC system used on later Hondas, different voltage regulator too. As that 250 engine ceased production in 1987, I doubt if big bore kits will still be available.

I have seen what it takes to make the 300 fourtrax fit in the frame yes you have to swap out the out put. Drive when you do so you have to drill out the end of the shaft after you cut it down about a inch so it will fit that and the oil feed tube will fit into the shaft hole you have to be careful about losing the thrust washer on the bottom. Of the gears when you pull the shaft out and put it in. However if you get get a 300 ex head with a 350d sleeve and get a 1988 300fourtrax cam its the only year that will work you bump yourself up to a 4 valve head put a big bore on it and the possibilities are endless. If you dont get that specific cam you will need to get a reverse grind cam becaauuse the motors spin in opposite directions of each other and will be catastrophic however big bores im interested in but almost aftaid to do they come with beer can cylinders that you dont want to get hot so youll need to get oil cooler biggger ported valves new clutch plates and pending on the cam you do go with you may have to get gas at the airport i could only imagine the cost of jet fuel lol