03 and maybe newer 03 CR250's how to:

[ProAMA725]

Thought I would stop back here and fix this thread. As a matter of fact, by doing this, you will gain all the low end you were missing, and it runs better from top to bottom. The 2003 CR250 only real flaw is the intake. Yes, it does restrict flow, and after you do this mod, you will see it is amazing (also the real reason for the "wah wah" feeling everyone talks about. gone and revs clean and tight). After testing the power valve like everyone else said, it still was slow. So I decided to look at the motor. The intake was tiny. So I got the drimmel out and razor and ported the intake like you would port a motor. After removing the middle bracket off the middle of the plastic insert and opening this intake up (both the plastic insert and the rubber was widened a lot and matched to eachother), the bike not only came alive. It also helped the jetting. (do not just remove white insert, it directs flow) It was less picky and ran clean everywhere, no need to waste money on a carb, all those problems related to it went away. Instead of all these motor mods, carbs and the likes. Just try this if you are unhappy with your 03 CR. I promise if you open up the intake you will say, what was Honda thinking. Every bit as fast if not faster than my 01 CR250 and my 03 KX250, both with pipes. (And remember, I do know bikes and do know how to ride, I've ridden a lot of bikes in my time and have tuned a lot as well.) All these engine mods and other things, everyone says has to be done so you can be equally powered to other stock bikes, is just wrong. I have rode mine in offroad and motocross. Climbing hills and jumping. It runs perfect. No need for overbore like I thought I would need. Don't even have a pipe on it. Now, other mods will obviously also help you gain added power, but if you are just looking for what is wrong with the bike when made, there you go. Mine is Stock, except for the free mod. Go figure... "experts"

Pics of my new 04 CR250 that already had a Vforce on it. Still had the same problem, until fixed like this. See how much more air can get through compared to stock!

[Woody_393]

Cool. Good information for sure.

Wonder if a previous year boot would fit on it?

[Woody_393]

Right on.

[Vintage Dave393]

Have you checked and adjusted the RC valve cables yet? It seems that this was a serious issue that contributed to the "wah, wah" effect on this engine. Any slack in them and the engine pulls like you are describing. There's also the Mikuni issue and that bike was jetted really rich at the OEM settings. I don't know how much of this the previous owner took care of, but it's a couple more things to look at.

[Faded]

Originally Posted by Woody_393

Wonder if a previous year boot would fit on it?

The ’02 cage/manifold will fit but it’s a step backwards IMHO. The ’03 design was better performance wise and helped to extend reed petal life.

Why didn’t you just take the stuffer (white block) out? FWIW, its size has a purpose and it’s not restricting air flow. None of these bikes suffer intake breathing problems unless your air filter is dirty.

There are gains to be had in the head; the squish clearance is overly large contributing to reduced potential power and increased octane requirements.

Changing the port timing to get an overal increase in power isn't too hard. By lowering the base 0.030" (0.75mm) and raising the exhaust port 0.060" (1.5mm) the bike will be a better overall performer. Be sure to relieve the squish 0.030" (or dial it in to your liking) to compensate for the removal of the base material.

I’ve posted the ‘how to’ for the 12mm adjustment for the exhaust valve that seems to give the best spread of power. A guy by the name of Henk Jager has the dyno sheets to prove it.

[Only registered and activated users can see links. ]

There is enough play in the clearance holes of the exhaust manifold that if you just let it hang and tighten it up there will be a mis-match between the manifold and the port. Make sure that your exhaust manifold matches the exhaust port before tightening it down.

The stock 48 tooth rear sprocket doesn’t help thing either. A 50 tooth on the rear makes everything better (unless you’re riding desert) and helps close the gap between 2nd and 3rd.

The replated big bore cylinders have a lifespan of two or three seasons before failing. You might have better luck with a sleeve though…

[Woody_393]

Anyone tell me why this shouldn't go to the KB?

[sandflyz]

Everything Faded said. Why? Cause i owned one. Welcome to the i just bought a 03CR and now i have to fix the motor thread.
I'm not being sarcastic i'm just tired of screwing with mine. By the way its for sale. I had head work done as well as ported the cylinder. Eric Gorr did the work, and it did run better. There are way to many issues with this motor to have to deal with in this day and age. Especially when there are so many choices out there.

I found a v force reed block helped
JD jetting or a different carb all together. An airstryker off of a 2000 CR will work nice. I opted for the JD kit it worked great.
You can try and bump up the compression a bit. The compression is low in these bikes to begin with.
Other than that just ride it and have fun.

The funny thing is that these motors were actually a generation behind the mid to late 90's motors that everyone is looking for.

With motocross bikes newer doesn't always mean better.

[Faded]

Originally Posted by sandflyz

An airstryker off of a 2000 CR will work nice...

I prefer and would recommend the PWK Airstriker off of the 1999 model, the only difference is the needle which has a 'standard' profile and is a better starting point than the 2000 needle.

Originally Posted by Florida 393

No KB for this one now, the originator can't handle a comment or a question.
Bill

[Florida 393]

Andrew,
if I could move just your replies I would, maybe someone that understands computers and the vBase software can do this. Or you could do a copy, paste and comment in the 2T KB and I will okay it "quick like a bunnyrabbit" (not you Hopper, settle down.)

Bill

[Woody_393]

hmmm.. I didn't see that coming at all

Faded, we'll get it moved over regardless.

[Florida 393]

Jonathan and Andrew,
See if this works and we can all share in the input here.

Bill

[Woody_393]

looks good from here.