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2001 CR 250 Rebuild

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Hi all, I just purchased my first dirt bike in December. A 2001 CR 250 with an original top end. I come from a downhill MTB background and am loving this new toy. Great training and covers a lot of ground. Calling it my "XC" bike.

Anyway, I've been getting horrible mileage (~10 mpg) and excessive 'splooge' out the tail pipe. Low end power is crappy too. This is what got me researching and made me decide to try a few things.

First I rebuilt the carb with the Moose rebuild kit. This didn't seem to help anything. Before and after the rebuild I had the carb set as follows (stock/as recommended by Procurcuit aside from clip position and float height):

Main: 420

Pilot: 35

Needle 6BEH1-73 set at 2nd from most lean position. Honda/Procurcuit recommend one clip richer.

Air Screw: 1 3/4 turns out from fully closed

S7 Needle Jet

Float Height: 17mm (Honda recommends 15mm)

The variances from what the manual suggested were my efforts to run it leaner. Seems to make not much difference.

Now I am in the middle of my next swing at the issue, which is to:

-Repack glass in silencer.

-New wet-side (right side) crank seal

-New stator side (left side) crank seal

-New Wiesco piston

-New spark plug

-New reeds

The old reeds look good except for one corner. See pictures.

Anyway, I'll post my progress and solutions/results. In the mean time does anyone have any theories on why this thing ran seemingly rich?

Cylinder Off.

slmuep.jpg

Looks pretty good, eh?

9l9zqc.jpg

The CRV is diiirrrrrty. Any advice for cleaning this? I'm guessing take it apart and degrease?

2hwi62g.jpg

Reeds, check out that corner bit. Could this be a partial cause of poor mileage and dripping splooge?

281hlrk.jpg

Best picture I have of the CR now, with the downhill bike in front.

2hxavqu.jpg

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Congrats on scoring the bike. I came back to this sport from a long run at MTB and also bought an '01 CR250 for my "XC bike". It's a potent rig. Mine is currently torn apart and I'm doing almost the same thing to it that you are. Sounds like you have the right step by step plan for diagnosing the rich condition which is freshen up the motor then start tinkering with the jetting. Have you bought a service manual?

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Damn that PV is gunky...you can soak it in gas to free it up a little bit. Old gas is fine. Leave it in there for a couple hours then go at it with a toothbrush.

FYI to change the stator side crank seal you need to split the cases. That one very rarely goes out though. You can test it by running the bike with the side cover off, spraying one shot of starter fluid at it behind the flywheel, and see if the revs increase. Yes, bad seal. No, good seal.

And yes, your reeds are long past done. Replace.

Did you clean the top of your piston when you removed everything or did it come out that way? The lack of any detonation or carbon deposits seems odd.

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FYI to change the stator side crank seal you need to split the cases. That one very rarely goes out though. You can test it by running the bike with the side cover off, spraying one shot of starter fluid at it behind the flywheel, and see if the revs

you do know this is a honda do yoo, and not a kawasaki?

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I am in the same process you are with my 2001 XC CR250! Check out my current thread about the build! My bike runs pretty well with the mikuni... I will have it apart and let you know what the jetting specs are inside it!

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Hardhit- I do have a Procircuit pipe and silencer on there.

Damn that PV is gunky...you can soak it in gas to free it up a little bit. Old gas is fine. Leave it in there for a couple hours then go at it with a toothbrush.

FYI to change the stator side crank seal you need to split the cases. That one very rarely goes out though. You can test it by running the bike with the side cover off, spraying one shot of starter fluid at it behind the flywheel, and see if the revs increase. Yes, bad seal. No, good seal.

And yes, your reeds are long past done. Replace.

Did you clean the top of your piston when you removed everything or did it come out that way? The lack of any detonation or carbon deposits seems odd.

Do you disassemble the power valve to clean all the bits in there? Or just soak the top of the cylinder and scrub from that access hole?

As others have since mentioned- that stator crank seal is removable without splitting the case. In fact, you can see it removed in that second picture I posted. I followed some advice on this forum to carefully drill two holes in the seal and pull it out with a pick. Worked great.

Another picture- The old plug compared to its new replacement.

nv6z9k.jpg

Edited by Cleetis

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Good catch. Didn't notice that about the CR's. Thought all dirt bikes had that on the inside of the crankcase.

I've always removed crank seals with two pilot holes and drilling in two wood screws, then grabbing with two vice grips and (put on some gloves here) yank the living fvck out of it. Always wondered why they didn't put dry side crank seals on the outside so you didn't have to split cases..

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Good catch. Didn't notice that about the CR's. Thought all dirt bikes had that on the inside of the crankcase.

I've always removed crank seals with two pilot holes and drilling in two wood screws, then grabbing with two vice grips and (put on some gloves here) yank the living fvck out of it. Always wondered why they didn't put dry side crank seals on the outside so you didn't have to split cases..

Honda did !

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keep up the work and google is your friend or on this site you can find any info you need

and loving the trek i have same one in green and black

how did you go about cleaning the pv and getting rids of all that gunk???

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OK. To clean a power valve or other gunky parts. Get yourself an ultrasonic cleaner. I"ve been useing one for years. Cleaned everything from bearings to carburetors.

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my favorite thing to clean the PV on my 01 is seafoam. i use Honda hp2 or motul and it melts it right off

How do you apply it exactly? Run it through the tank or through the air box or something?

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You need to remove the power valve assembly and soak all of the parts in seafoam. Then you'll be able to get a hand/rag/brush inside the cavity and clean the rest. Be careful there is a rod that goes all the way through the cylinder to the bottom end on the front right side. It goes up into the powervalve down through cylinder and connects right there at the bottom end. At least that's how it was on my 98', but refer to your service manual for removal. You'll also want to pick up some honda moly 60 paste at your local honda dealer for re-installation. The manual will recommend it as well.

Another thing you can do once you have the cylinder off and powervalve removed is take some 600-800 sandpaper and wet sand the "intake" inlet that the reed block goes into. It's basicaly a port and polish, and just make sure you do a nice even job until it's nice and polished inside there. Just a couple tricks I learned from a pro buddy of mine. It somehow helps with air atomization or something, whatever port and polishing does lol

I'm no pro mechanic or anything but this is just what I remember from when we did my top end this past december 30th. If you can afford it, I'd grab an hour meter also. I'd also highly recommend boyesen dual stage pro reeds as replacements ($40) and boyesen is the best. Exhaust packing is so cheap ($7) and may take 30 minutes or so to do. You also may want to put a bead of hi temp silicone around the silencer jug once you have it apart right where it connects and bolts up. We forgot to do this during my rebuild and once the new packing got soaked with spooge I began to have a leak through the bottom bolt hole, so I took it apart and installed the hi temp silicone and it worked like a charm.

Edited by BlackCR25098

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Got it, thanks. I wonder how well that works at cleaning out 2-stroke headers?

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How do you apply it exactly? Run it through the tank or through the air box or something?

no i take the power valve out and pour seafoam in a coffee can and let it sit, i works better than gas and is safer, while thats happening i take wd-40 and a blue or green ( not red black or gray) scotch brite pad to the bore and deglaze it then i take the same things to the power valve flaps, rods i clean the bearings and springs with b12 chem tool , then i was the whole cylinder out with hot soapy water and a tooth brush

as far as im concerned thats the real way to do it

Edited by terrobelone

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Got it, thanks. I wonder how well that works at cleaning out 2-stroke headers?

get a map gas torch and burn the carbon off first use the old seafoam from the power valve cleaning to rinse the pipe out, i just did this the other day worked great, the carbon will glow red when you hold the flame to it, so you know where you need to burn it off, if it crackles and pops when you do it, then you have waited to long my friend and will enjoy a little more pep

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For cleaning this power valve I completely disassembled and spent way too long scrubbing all the parts with scotch brite and using a dental pick to remove the carbon build up. Also used engine degreaser.

Does anyone have any tricks for tightening the clutch center bolt? I'd rather not buy the $35 tool to hold it steady while tightening the nut.

The Wiseco manual has a section on drilling lubrication holes in the piston if your 2-stroke has an exhaust bridge. I'm pretty certain this bike (2001 cr250) does not since I don't see one in the cylinder. Everyone agree on this?

Edited by Cleetis

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