so, after racing my 03 cr250 all fall and spring i have noticed some stuff. first off, my bike seems to have only a mid-range hit, not much else. definately not a yz engine. i race against mostly 450's in vet classes, its tough to give them a front wheel as they are very fast, low,mid and high-hard to beat. basically my stragedy is to out corner them and jump where others wont. Need to find some power w/o porting the engine into a light/switch powerband.my bike doesnt run poorly, it seems its just overmatched. anyone have any ideas?

try freshening up the engine?
the cr250s i rode were all top end light switch power. if its just midrange, maybe its a power valve issue?

or just buy a ktm

have someone build you a custom dome for the fuel you run.

Port the bike from a reputable source. should be a 5hp gain here if done right.

taper bore the carb for more topend.

could also run a adjustable ignition to tune the curve how you like.

lastly tuning the bike with proper plug chops, changing needles and getting everything just right makes a huge difference.

well, engine was freshened up-lol. low hr machine, new wiseco 2 ring piston, new reeds, tmx carb with 110 race fuel, changed the nozzle re-jet etc.. like i said , the bike runs good just not enough for the 450's. the more hardpacked the track the tougher it is too keep up, i spin and they motor away. Porting the bike may bean option, just leary of making it unrideable.

This thread is about an 07 but will also apply to an 03, if you go about 10 pages in CamP talks about taking .30 off of the bottom of the cylinder which lowers the exhaust ports giving the bike more low end power.  If you turned down the bottom of your cylinder and then had the head cut for squish and whatever type of gas you want to use, it would make the power more usable.  Then get a PWK airstriker carb froma 00 cr250.  These mods make the power more usable.  By the way Eric Gorr will do the cylinder and head work for $75.

http://www.thumperta...8-new-07-cr250/

Edited by frdbtr, 05 July 2012 - 07:15 AM.

you aren't going to keep up to 450's on hardpack unless you are a better rider or ya drop a 500 in that frame.

I've been thinking about putting a FWW in my 250 just for better traction...nothing too heavy maybe 6 or 8oz. Curious to see how my bike will respond to it.

You're going to have to out ride them not out run them.  , but as has been mentioned the PWK has been very popular for a more temperature stable jetting than the tmx, with most reporting better bottom end response, and close to equal top to the mikuni.

Put a FMF Gnarly on it and maybe a FWW if you ride hard pack.  They should be killing you on that stuff in the turns.  Pro-Circuit pipe is not a good choice for additional low-end power if you have that.

I went thru something similar when I first bought my 02 & 03.   I was doing some local racing against the new 4t bikes back then & wanted to be able to compete against them.   I tried different bolt on combos pipes, reed cage, carb tuning etc.. but all they did was move the powerband around.  What worked for me was having some cyl. port work done & reshaping the cyl. head.  Those mods yielded the most gains & really woke the motor up.   The motor now has a wide useable powerband with an extended overev.   I'd recomend looking into a reputable engine tuner & have them do the work.