chris the os carb is the best, easy to tune ,holds a tune,motors are priced right. if you plan on racing in the future a 21 is as big as you can go with the buggy,a 28 in truggy. but if your just having fun os just came out with a new 28 that i hear is a beast. the italian motors are harder to tune,narrower window,take longer to break in,parts are more,