The fact you are asking this question is 100% proof you should not buy the bike. An RS125 is a sensitive, finicky, highly tuned, expensive, knowledge intense rocket of a minibike. This is evidenced by the fact that NO ONE still races them. They are dinosaurs. Super fun, fast, razor sharp dinos.
Get a Ninja 300 / 400 or R320 and you will have a blast. Spend $2500 for a well sorted one and you'll never really need to put money into it. We bought a bone stock Ninja 250, put $600 of race part on it, raced it for 2 years with stock pipe, air filter, and one oil change a year. It outright won some sprints, and we actually won a 4 hour endurance race at eagles canyon on it.
But stepping up to a 300 or 320 gets you fuel injection, so you don't ever have fueling issues, or carbs to clean.
And, despite the critics, nothing is more fun than running advnaced group lap times on a 320 or 300 at MSRH dipping into the 1:49's while never going over 100 MPH.
Also, I believe Ride SMart finally got their heads out of their and started allowing 250's and 300's in Advanced so you can ride for half price on your "mini" if you have a cmra race license.
Whatever you do, DO NOT buy an RS125 or any high strung 2 stroke. It is a lifetime of misery spent wrenching, tuning, plug checking, premixing...but not riding, not racing.
Go on Scott Finning's Leightweight Motorcycle Roadracers page and ask the same question. And for what it's worth, my little 250 has been the bike against pit wall in the profile pic for like 10 years.
In full disclosure, the sprint races were won by our ringer, who also won Pikes Peak on a MV 675. but I was only 1.5 seconds off his race pace. And I'm a novice license holder.
A video of fun 250 stuff at TWS (Texas World Speedway) I made chasing Mark Shim, both on 2008 era 250's.
BRAWP it like its hot, BRAWP it like its hot.
