it would be crime to put a different engine a 250R. And 2-strokes may need to be rebuilt sooner than 4-strokes, but they make more power, thats the trade off. But i have yet to have a problem with my 250R. It starts first kick every time, and runs like a champ. The onl yissue though with buying a 250R is that the frame has the potential to crack. Nothing major but little cracks will start pooping up, just due to the fact that they're 17 years old. If you have after market shocks and stuff on your 400 i would say just get the 250 motor for it. Just maintain everything and you won't have any problems.

 

i have about $4000 stuck in to mine but still have the stock shocks, a-arms, frame, swing arm. the 2 most expensive things on my 400 is the lonestar axel and the hard core front hubs.

 

I hope you meant $400, because i don't know how you would have $4,000 in it without aftermarket shocks, a-arms, and swingarm. If you only have the axle and hubs then a race ready 250R might be just what you're looking for. If you do go that road, be ready for a little more work to maintain it. But believe me it will put a big smile on your face.

 

the midl 3000s i have about $500 of spair parts laying around and bout 3000 sumthin on it

ITP RIMS
KENDA CLAW TIRES ALL AROUND
LONESTAR AXEL
HARDKOR FRONT HUBS
HOLE SHOT HD BACK AND XCT FRONT TIRES
NACS PARCKING BRAKE BLOCK OFF PLATE
BLUE SHOCK COVERS
CLUTCH KIT
K&N AIR FILTER
AIR FILTER CONVERSON BRACKET
DYNO JET KIT
WATER REPELLENT PRE FILTER SKIN
OMF SEAT BRACKET KIT
DG BUMPER
DG NERFS
WHITE BROTHERS E-SERIES MUFFLER
MSR DOMINATOR BARS
LONE STAR SPROCKET HUB
OMF AIR SCOOPS
POWERMADD HAND GUARDS
CRJ WHEEL SPACERS
LONGHORN BIG BAR
BIG BAR CLAMP
MAIER BLUE BACK PLASTIC
MAIER BLUE SIDE PANNELS
MAIER BLUE GAS TANK COVER
MAIER BLUE RACE CUT PLASTIC (uses lights)
MAIER BLUE RACE FRONT PLASTIC (uses no lights)
NACS HEAD LIGHT GUARDS
MOTION PRO CLUTCH CABEL
K&K NUMBER PLATE BACK GROUNDS
909 GRIPS
NACS SEAT COVER (on now)
ONE INDUSTRIES SEAT COVER (not on)
NACS GRAPHICS (on race plastic wit no lights)
ONE INDUSTRIES GRAPHICS (on plastic with lights)
BILLET ALUMINUM GAS CAP
PRO TAPER BAR PAD
nacs footpeg extenders
6 rad light (were $15 each)

 

I've had my 440 kit in my 01 400ex since about a week after I bought it and have had no problems what so ever. I dont have a real high compression piston in it which may be the difference but it runs great every year.

 

well if i kep my engine i would bore it to a 416 or 425 and then buy it a stroker kit

 

i put an xr650r in my 400ex and it is great it doesnt vibrate at all the engine is counterballanced ill post pics when i figure out how

 

I would most defiantly steer clear of motor swaps for the most part the frame was designed pretty well for the engine that is in there...not only do you have to have parts made ...like mounts..possibly clearance issues, electronics ...ect and when you do get it all in there you resale value goes to hell. And not to be rude but it doesn't seem like you have a lot of experience with atvs, just repeating things you may have read, to do a swap it would take considerable knowledge and thought for it to work out well. Just my thoughts on the situation.

 

That looks like a nice bike. I bet it is a handfull without a swingarm.

 

If you want a crf ATV FOUR PLAY can build a great crf frame. heres there web site www.atvfourplay.com