RM250 tips

[Project300EX]

I got an '88 RM250 bottom end off of Ebay and it's supposed to have been shipped out yesterday. Supposedly the only thing it needs are new bearings, but I'll probably go ahead and redo all the seals and stuff while it's broke down. Since I'll have to buy a cylinder and head I'll probably do a few things to it for performance. What all would you guys do to it? I'm looking for it to be real powerful, but reliable and trail worthy. Here's what I'm thinking.

FMF fatty pipe and Power Core II silencer
Athena complete gasket set
69mm Wesico piston assembly
LA Sleeve
Moose Racing crank bearing/seal kit
Boyeson Power reeds
38mm Keihin carb
14/36 gearing

About how much power would this be putting down? Also this is going my 300ex project.

[Project300EX]

Any thoughts?

[Project300EX]

Bump, somebody has to know a little about these old two strokes.

[joshyz125]

what are you building it for?
Woods or WO Sand stuff?

[joshyz125]

i didn't see the trailworthy part,

Depending on how much time you want to put in it, you could clean up the imperfections in the cylinder ports,
you could port it, polish the ports, but there's alot of opinions on porting and polishing, you'll have to research that and get go your own way.


a flywheel weight is a good thing in the woods.

how much money are you wanting to spend.
speed cost money, how fast do you want to go?

[Project300EX]

It's a budget build. I would like to be really quick, but still retain decent reliability and trail capabilities. I've heard stock they're from 40-45 HP.

Edit: Also that piston I listed is 2mm overbore.

[joshyz125]

i couldn't ride a 250 bike to it's potential, If it was me, i would put good name brand parts in the motor, with a flywheel weight, and spend the rest of my money on suspension and a steering stabilizer.
Best mods you can do for the woods IMO

Another thing is i'm a HUGE Fan of the new 4 strokes.

[Project300EX]

Originally posted by joshyz125
i couldn't ride a 250 bike to it's potential, If it was me, i would put good name brand parts in the motor, with a flywheel weight, and spend the rest of my money on suspension and a steering stabilizer.
Best mods you can do for the woods IMO

Another thing is i'm a HUGE Fan of the new 2 strokes.

So what do you think about the list I made? I would have to buy those parts anyway, since I'm starting with a bottom end.

I've already decided on the rest of the quad.

[joshyz125]

They're all name brand stuff
pipe and silencers are always a good upgrade, and doesn't hurt reliability.

as are the rest of the parts you listed, i wouldn't be scared to put that stuff in the motor and not think it is going to start everytime.

[Project300EX]

Originally posted by joshyz125
They're all name brand stuff
pipe and silencers are always a good upgrade, and doesn't hurt reliability.

as are the rest of the parts you listed, i wouldn't be scared to put that stuff in the motor and not think it is going to start everytime.

Thanks. I was just wanting to make sure it would be a pretty good combo. Any idea of what kind of power it would be putting out with those? Also would that be good gearing for a 300ex based quad?

[joshyz125]

As far as accuall HP, i would be COMPLETELY Guessing, if you want to know for sure, build it, and i'm sure there's somebody with a dyno within driving distance that would be willing to check it out for ya.

On the gearing, i would also be guessing, tire sizes, and all that have to be calculated into that.
and you'll probably have to play with it a little to get the most out of it.

[Project300EX]

Alright. Thanks a lot man. Sorry for all the questions, but so far you're the only person that's shown interest.

[joshyz125]

no problem, hope i helped a little anyways