I posted this in the Kids section 1st, and got some imput, and thank you.
My sons Kymco 250mxu, needs a little bit more.
The OEM carb is 18mm, which I beleive is too small for a 250cc engine. My daughter's little 150cc has a 24mm carb.
I have installed a Kiehin PE24 on the 250 and it runs fair. but it has a #95 main jet, I am going to buck it up to #115 and see if it helps the top end. Any thoughts.

 

You'll have to do a few plug chops, and base the jetting on the color of the ceramic part on the firing end of the spark plug. You can check the idle mix by just letting it idle for a minute, shutting it off, then pulling the plug (let it cool off a little first). White indicates that it's too lean, Black means that it's too rich, and if it's tan or light brown you're right on target. The same goes for the midrange (ride it around between 1/4 and 3/4 throttle for a few minutes, then kill the engine before you release the throttle. Then for WOT, do a wide open throttle run for as far as you can without breaking any laws (try for at least 10 seconds at full throttle. If you don't have enough room to do this, then run as far as you can wide open, turn around quick, and do the same thing again, then kill the engine, coast to a stop, and check your plug. That'll give you more to go on than just guessing. To me, going from a 95 to 115 seems like a really big step. If the jetting was that far off, it probably wouldn't have ran at all, or ran like it was running on an empty tank.