hey guys im a newbie to the forum i had a cbr250rr and it got written off in a crash so recently brought myself a nsr250r/mc21 and its great, a bit more of a dog than the cbr but heaps more fun, anyways i recently done an a modification on my airbox noticed it goes better heaps more noise from the engine aswell which is a good thing but i when taking off from lights and crap gotta give a few more revs than normal, so just wondering have much people done this mod aswell? do i need to get it rejetted? any advice on this would be tops and what other kind of mods are good for it?

Hi '69, welcome to the forum.

Good choice of bike - don't forget to vote for it!

There's a load of info on this site as to how to tune your bike, and modding the airbox is a good place to start.

You will probably be okay for jetting if all you've done is the box, but to be sure you really should pull a spark plug and check it's colour.

Best bet is to surf the site and read all you can. Then if you have any further questions get back on here and give us a shout.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

a bit of a dog??? compared to a 250 4 stroke!?! you must be kidding...

have you ever had the tach above 8000RPM on your NSR?

its a 2 stroke so its not gonna have the torque down low
but this should be more then compensated for when you ride between 8K - 11K RPM

keep us updated
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Koren
2 Strokes and I'm Off

I was assuming he meant the condition of the thing, not the power delivery.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Modifying the airbox will need rejetting. It'll allow more air into the motor at high rpm which will lean things off. Consider going up at least a couple of sizes on the mains.

Dave's spot on with his plug chop theory. Heed his advice or you could run into trouble.

Let's not knock the CBR250RRRRRRR though. There's not many bikes that can cruise round town at 15,0000rpm. Oh yeah, and don't let me borrow it 'cos I tend to just hold the thing in first gear with the valves bouncing at over 20,000rpm, laughing my head off. They're fun

nah, its good as condition, just the whole power deliviery thing and yes i have had it above eight grand it goes nuts, maybe i picked the wrong word to describe it, what i mean is its not the smothest ride in the world but thats whats so great about it just all the vibrations and the angry two stoke noise, cheers for the tips on spark plugs and everything.