right size carb?

[fomospede]

hey guys weve been testing and getting tuned pretty close
but im wondering if i should change carb from a 21 to a 24?
sport pro s6 70cc cyl, stock crank
malossi overange
pcs pipe

thanks for your input

[nitrofish]

Hey Fomo. The 21 can work well if not better in some situations. Rule of thumb, a larger carb is going to work better upstairs with losing some low or drivability. I would base it on a few things. If you are turning higher rpms due to pipe/cylinder combo go with the big. If you are running wide open due to track size and rider, run the big. Take into consideration gearing and rider weight. There is no magic formula, it is what your set-up likes and where you want the bike to perform best. I would dial your 21mm in, do some timed sprints and record the data. If funding permits pick up a 24mm and do the same. Run the small on tight tracks or even mud bog kinda days and switch to the big on the wide open deals. Don't get caught up in the bigger is better or what everyone else is running. JMO. Matt.

[jerkyboy]

Ive run a 21 and a 24mm carb on the same motor and performed better with the 24 hand down. Lost alot of topend with the smaller carb.