All depends what you are doing for your build,. Im not 100 percent but i think thinner is for low and the thick if for mid to top end. This is from Esr link,
http://www.eddie-sanders-racing.com/product_p/esr reed block 2012.htm

 

I'm trying not to spend a lot more money on this quad which carb should I use my tuner says it doesn't matter because he will set with the o2 sensor the 34 fits better and cable seems to fit better in the quad any opinions

 

I would use the 38 MM carb, even on a stock cylinder it will run better than the 34 MM. As far as the reed spacer plate goes, you won't see much if anything on the Dyno with reed sacer plates 3/8" or under. Reed spacer plates are used more to improve 'fitment' from the carb to the intake box boot, and to help save reed pedals.

Carlos

 

38 MM carb is best option for and I too have seen my friend using the same, I will post the image if I remember while meeting him.

 

If you have the coin I would Invest in a smartcarb they are pretty steep price wise but the fact that you dont have to mess around with jetting is worth every penny IMO

 

Hold off on the Smart Carb.....the product is new, and has had very little testing to date. From what I hear and see it has potential, however, I also hear mixed reviews....the jury is still out on the Smart Carb IMO.

Carlos

 

Just out of curiosity, what kind of bad or questionable reviews have you heard about it?

 

I put the spacer In using the 38m carb and boot from upp also got the correct cable a dgh needle 48 pilot and 160 main from BDT the other day its running great I just dropped it off with riddle powersports to set it up using an O2 sensor he has tuned my banshee and raptor has worked with several 250r over the years im looking forward to ridding it this weekend

 

Just out of curiosity, what kind of bad or questionable reviews have you heard about it?

Just a lot of unknowns, not enough positive info yet available for the 250R as most are just receiving the carbs. The negative I have heard and seen has been on engines in the BB category, that is 330CC and above. Seems the Smart carb has issues feeding the requiered amount of fuel to keep these BB engines from going lean. The Smart carb folks are aware as they have been sending different needles, and options to deal with the BB iissues....

Again this is very limited information to date, that is why I recommend waiting till more info is posted or available.

Carlos