Becoming a wheelie boy yz250 supermoto

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Sorry man , I read the " wheelie boy " part in the thread title , and wasn't qutie sure what that had to do with Moto or supermoto. Fwiw , it does sound like a good plan , and I hope you figure it out and have fun with it.

Sounds like Jeffro rolled this guy a fatty

I'm not sure if I did or not , but being sunday night , I wish I kinda had one.

Cons: The engine isnt conceived for street use. If you cruise at 50MPH it will be hard on the taller gears . The SM Set up will be hard on your entire drive train in general. It's fine as long as it doesnt go bad on you when you really need it, big jumps and stuff. You will also need a different front brake, separate chain and sprockets. just something to keep in mind.
You are talking about the two stroke right? these engines dont like to be run at a constant RPM, changing top ends wont be enough. I am not a doctor but i am confident the vibrations will make you unable to have kids after only short exposure.
Pros, it will be a lot of fun while it lasts. Trip Carlyle would be proud.

I did something similar 20 years ago. It’s not a challenge to do. The motor will be fine. Maybe go up a little with jetting to be on the safe side. As was written above, you’ll need a different (shorter) chain, a bracket to space out the front caliper if you decide on a bigger disk. Maybe see if you can use a rear wheel with a cush drive to help with engine hunting on a steady throttle and assist with backlash. Oh, and a bicycle speedo.

You will have fun dude.

I made a street legal CRF450 back in the day and it was a blast. I couldn't control my inner demons on it though and had to take it to the track after a few too many close calls on the street.

When I was riding on the street there was a couple of guys in our group who had created 2 stroke 250 SM's and they didn't seem to have too many issues. Remembering to always always carry along a pre-measured bottle of oil when it came time to hit the gas station was an issue for them. They got pretty good at eyeballing it though. Vibrations didn't seem to be any worse for them than it was for us on 4 strokes. Locktite is your friend, and if your exhaust hits your license plate in any way, you will lose the plate at some point.

The only person I knew that ever had an issue with their transmission was me, and that was from trying to run an aftermarket wide ratio on my CRF. Ate two of them before I went back to stock and learned an expensive lesson along the way. It was cool to get a 450 up past 100 MPH though. That was even with a slipper clutch to reduce the load on downshifts, which won't be an issue on a two stroke.

If you can get an offroad model with a wider ratio transmission, definitely go that route. Gearing them for highway speeds makes the lower gears almost too tall to use. You will burn through clutches like mad trying to get up to speed from a stop. Having a little taller top gear means your first gear doesn't need to be so tall to run at highway speeds without being tapped out at all times.

If you do a street driven 2 stroke make sure it runs a tad rich off Idle.....decel seize is not fun