I have always been told that 1200 is where you want to run exhaust temps..., but some will run them hotter-leaner to get performance out of the motor....Leaner is also sooner on a rebuild...I ran a shifter kart motor at 1200 all season and my friend even did real well at nationals 2nd place, when we took the motor out and sent it to Swedtech they where surprised how good it looked after a season. at Nationals the swedtech motor guys ran it up to 1300, but at that point engine longetivity is not a player.....D