I have a Ct 330 big bore kit in my 250r. I'm running a 39 PWK right know but am thinking about putting my 38 Air Stricker with reed spacer and power now for my CT 310 bike on it. Does anyone know if I will gain anything or lose anything by chaning this set up. If so where will I gain or lose.

 

You will probably gain a little low end & lose a little top end. Also depends on what pipe & porting you have.

 

Dont bother. It wont make that much of difference unless you really want to try and chang the power band. a 39 is good. who did the porting and for what kind of riding?

 

I agree. BOTH of those carbs are going to be somewhat similar. I believe you won't notice much (if anything) by going to a carb that is 1mm smaller.
I run a 38MM airstriker, and my friend runs the 39MM. IMO, they are pretty comparable.