We are in Valencia Ca. As far as a new carb I would say the 750 is plenty but the 850 would work as well. Proper tuning is more important than a 100 cfm difference. If you go with a new carb keep in mind fresh fuel and clean fuel filters are equally important. Also remember at this point without actually witnessing the problem we are all just taking guesses as to the cause. Maybe a plug wire is bad or timing is off. Based on your description I'm betting on carb but I can't make any guarantees without seeing it.