Hi, I´m new on this forum and I´m from Sweden, so I hope my crappy english will be understandable.

Anyway, I´ve just bought me a MC18 NSR250 SP -89 and I want to make the wire splice to remove the restriction on the RC-valves.
But I don´t know very much about jeting so I thought I´d turn to you here on this forum since alot of you guys seem to know what you´re doing.
First I wonder if it is enough to just fit bigger main jets, or do I have to do more than that? If so, what other things? and also, how big are the original main jets and what main jets would be around the right size after having made the wire splice?
One other thing, I also read that the filterbox restricts the airflow a little and therefore it would be a good idea to mak 4x1" holes on top of the box, so I was thinking of making that mod too if nobody disagree...

I also want to lower the front suspension around 2" to make the bike look more aggressive, so I´d like to know if there is an easy way of doing this without having to sacrifice too much handling.
Do anyone have any idea of how to do this ?
since I haven´t picked up the bike yet I do not know exactly how the forks are built, but I was thinking of cutting off 2" of the fork on the top end and cut the springs in the same length.
Is it possible to do this? or is there another way?
Also remember this is the SP model

And one last quick question. Is it possible to fit a mc21 seat cowling on a mc18 bike with little or no modification? If anyone has done this befor, does anyone have photos of the bike?

Thanks in advance

/Stefan

Hello and welcome, your english is good, don't worry about it

Stock carb settings are here. Std '18 is 128's.

4 1" holes in the airbox is a good idea.

Just bigger mains will be fine, Steve's the man to tell you how big, from memory not much different (if at all) from standard.

Lowering the front is another matter, you'll be able to do it by just dropping the fork legs through the yokes but you'd be better off raising the rear instead as the MC18 fairing hits the floor at serious lean angles anyway.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

With 4 x1" holes in the lid running stock pipes 130m/j is normaly enough. If your running race cans on stock pipes run 132m/j.

Lowering wise, as Fontyyy says. Best lift the rear. Look in the workshop and you will find a drawing of the HRC linkages. Make a pair of these and this will lift the rear almost a full inch.
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If I have to take the carbs off once more...

Ok, thanks a lot for the help

the bike is currently fitted with hindle race pipes but since the midrange power suffer because of them I'm gonna refit the standards så I´ll just try with the 130 and 132 main jets

Also, did anyone know if it´s easy to fit the seatcowling from an mc21 on an mc18?