[mxzsnowman]

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  

 

[summit 670]

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

 

[1000-IMP]

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.

 

[pinnerx]

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