I am considering having PSI bore my carbs on my 670. *I am a little hesitant as I am concerend about the reliabilty factor as I believe you would be pushing the motor harder. *Has anyone had any luck doing this and did you notice much gain? *PSI would go from 40mm to 44mm.
Thanks in advance * http://www.snowmobileworld.com/forums/iB_html/non-cgi/emoticons/wink.gif

Taper bore is the only way to go!! Maintains low end and gives you the top end your looking for. Best of both worlds!!

If I were you I would just buy a set of used(or new) 44 mm carbs, keep the throttle response and not have to worry about all the other variables, with the added benefit of flowing more air.

I agree with 100-imp, also if you go to bigger carbs you'll have to open up the carb throats on the rotary valve cover to help with the increased air and fuel flow