03 cr250

I recently purchased a 2003 CR 250. When i test rode it i was mostly in power band. I got it out in the hills and noticed a low end bog. It runs beautiful in the top end but right before power band kicks in if i hit the brake and punch it it bogs. Ive adjusted the ring on my needle. Ive changed spark plugs. it came with a 390 main jet and i tried a 420. it was worse. the guy i bought it off says it ran awesome before he parked it. If anyone has any suggestions or help please let me know.

I'd try adjusting the air screw (more turns out)

ive tried 1 thru 4 turns. it runs best at 4. its sapose to b 2 1/4 turns out. its got an fmf gnarly pipe and silencer. It has a boysen rad valve as well

go into the honda 2stroke page. what your experiencing is normal for the 02 - 07 models for a few reasons. do a search for 03 cr250, lots of info you need to know if your serious about improving your problem .

i went to the pages you said and couldnt find much. lotsa info but not much about the low end bog

The suggestions I've seen are to put on a bigger rear sprocket (51 tooth or so), put in a Vforce3 reed and use a ProCircuit pipe. I don't know how the Rad Valve compares for bottom end...

But it was working fine before last winter

My buddy parked the bike in September of 2010. It ran great. I bought it in April and it had not been started since sept. I test drove it and may have ran dirty fuel in it. When I got it home I changed tranny oil and fuel. I ran iT 40-1. And ever since it's had a low end bog. The reeds in the boysen rad valve look great it's something that happened while it's been sitting because it ran nice. I rode it when it was his. I put a new air filter on as well. Would dirty fuel wreck somethIng

Did you ride it back in Sept of 2010 or are you going on what your buddy said? Have you had him ride it recently? Is it behaving differently from what he remembers from before?

If it's not working the way it used to, it could be that the carb is gunked up. Some fuel/premix combos can really leave a bad coating inside the carburetor if they sit too long, especially in the jets...

The suggestions I've seen are to put on a bigger rear sprocket (51 tooth or so), put in a Vforce3 reed and use a ProCircuit pipe. I don't know how the Rad Valve compares for bottom end...

Good advice.

From what I been reading, the Rad Valve and the Vforce3 are about the same. Some people even say NOT to buy either one. They don't make that much difference to justify the price.

Best mods seem to be the Pro Circuit pipe, and the larger rear sprocket.

Everyone recommends that.

Definitely clean out that carb. That would be the first thing I would look at.

Check our power valve cables and actuator

Thanks guys il try a couple of these suggestions

Would carb clean get rid of this gunk cause I've taken it apart and cleaned it about 5 times now. I have moved the clip on my neeDle thru the top 3 grooves and they all sound the same. I did riDe the bike last year and it it running different than before. New top end has maybe ten hours on it would anyone suggest new rings or piston.

But it was working fine before last winter

Your fuel turned:busted:

Go to Advance auto and get a gallon of carb cleaner, take your carb completely apart, follow the directions on the can, submerge up to but not the plastic (TPS) and blow all holes with compressed air.

then most important - Check the float height.

your problem is NOT normal, at least not with my 05

you really should "Winterize" your bikes if you don't ride them.


I have a 2004 and I didactic few things and the low end bog is gone. I started with the boyesen exhaust flange which did nothing. Next I installed the JD jet kit and ordered a pc platinum pipe. Bingo! The JD jet kit transformed the engine! Running Blendzall racing Castor at 32/1 with 1/2 premium fuel and 1/2 VP race gas. Runs awesome! Next tried the Pro Circuit pipe, wrong move, stock was better so changed back. Swapped the 48 rear sprocket to a 50 and I don't like it...changing to a 49 next. Hope this helped!

After cleaning and inspecting everything from Reeds, air filter, float level, pv cable adjustment, etc try this jetting spec From Boyesen.


Application Rad Vlv 02 f

Main 370-380

Clip position 2

Pilot 32.5 -35

Air screw 1 1/2 -2

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