I would like a 39 or 40 tooth rear sprocket for road use. Does anybody know where I could get one?

 

wow, smaller sprocket? stock sprocket is undersized for the stock horsepower as it is... you do alot of downhill riding?

 

You might just try a 15 tooth on the front. Two reasons. One, its cheaper to try out to see if you will like it, and two its cheaper if you don't like it.

 

+1 on the 15 tooth. Just put one on my klx yesterday. Now it's set up as 15/42. It cruises in 6th gear at 65 mph (GPS) at 6K rpms. When fighting a headwind 5th gear keeps it comfortably at 60 mph at about 6.5K rpms. Cost was less then 10$ and is easier to install.

 

With a small windshield the 250 is just fine with 15/42 for street use. Don't think I'd go with that gearing if I was using it most of the time in the dirt though.

 

I am currently running 15/42 and with the (Bill Blue) Big Bore 330 and pumper carb, it still easily pulls wheelies in first and second. I bought a set of used wheels off of e-bay that I put street tires on and would like to run a smaller rear sprocket on those wheels. The stock chain is set to 1 1/2 on the "snails" running 15/42 so, I would think 14/39 or 15/40 would work fine with the stock chain... making wheel swaps simple.

What other bike has the same rear sprocket?

 

how is the take off from a light slugish or ok with the 15/42s

 

I give it a few more revs when starting out but it handles it just fine. I did kill the engine on the first ride with the 15 tooth but I'd forgotten to shift from 2nd into 1st. 2nd gear is not too good from a stop.