2003 CR 250 fouling plugs

[kportingale]

hey everyone,

i just bought my first dirtbike a couple of weeks ago, a '03 cr 250. the last ride i was on (only trail riding) after a couple hours of riding i came to the bottom of a long hill and suddenly the bike was running like it was out of gas, then it died and wouldn't fire up. turns out the plug was fouled ( put a new one in it 2 rides prior) so i put my old one back it and it ran for about 30 min then when i tried to start it up the next day it wouldn't. put a new plug in it, ran for about 20 minutes then i could barely make it up the driveway. pulled the plug and it was black and a bit wet. I'm not new to mechanics but i am new to two strokes, any help on the matter would be much appreciated. thanks

---------- Post added at 05:27 PM ---------- Previous post was at 04:56 PM ----------

so i just checked my tranny oil by removing the screw and the level seems low cause when i changed the oil ( a week ago, maybe 5 hours) i filled it up till it was coming out of the the screw hole. when i just undid the screw i had to lean the bike over a good amount till some came out. do these bikes chew through oil like that or is it a good possibility that the crank case gasket it screwed and i'm getting oil in my fuel. i heard that that could also be a reason for fouling plugs. thanks

[RCPH]

Not sure, but I would suspect a couple things or a combination of things.

On my 01 cr250 I went one jet size leaner on the main and pilot jet. I also moved the needle clip to the highest position.

Even after that it still would foul plugs and worse, it almost sounded lean. I put the stock Main jet back in and put the clip down a slot and bought a different size needle.

It was better but still not perfect. I ended up selling the bike to a friend (I had bought a 4s). Who found the final cure on top of all that I had done. He changed the pre-mix brand and ran a slightly leaner oil ratio (I ran 32:1) and I dont think he has fouled a plug since.

Good luck !

[hondatwosmoker]

I own an 03 CR250 as well and expirenced very similar problems. When ever I came down a hill my bike would load up and bog,like it was fouling a plug. I tryed going leaner on the main all the way to a #380 jet and put the clip all the way to the top on the needle. This helped some, but it really just gave me more time to ride before I fouled another plug.I also changed my crank seal fearing this was the problem, I cant tell if this was the problem cause it still fouls plugs, and uses a tiny bit of oil. You should replace your crank seal if you are losing a substancial amount of oil and then try going leaner with your jetting. I personaly was tired of fiddleing with the mikuni carb to no success and so I caved in and ordered the Keihin carb.

[tchui]

hey, jetting is a common difficluty on that bike, however bad 'tuning' shouldnt reult in more oil consumption. myself id check the crank oils seals first, then go smaller on the main jet and leaner on the premix. 40:1 is what i run.
heres another thought 03 bike so you bought it used? new to dirt biking? is it possible your piston/rings are shot and the lack of compression is letting oil through the stroke and fouling plus and buring oil? does it smoke alot?

first time my plug went was also on the trails and i was told its cause i ride too slow

[crguy]

worn rings will not make it smoke more, it's a 2 stroke, they burn oil to run and don't have engine oil to burn (unless you have a bad crank seal). As far as plug fouling, if you get it figured out let me know. I unwound the choke and took it out and it ran like a dream with one size lean main and the needle leaned out. However, can't run like that cause its unfiltered air.

[kwmotocrosspunk]

id check out the crank seal, could be worn out allowing oil in the combustion chamber and just for fun id do a compression test and maybe a leak down to see the integrity of your motor

[kportingale]

so i drained my oil out and found out that i didn't actually lose any oil. my carb is running stock jetting and i'm getting spark after i clean the plug up. gonna try running a different ngk plug cause my friend had the exact thing happen to him today on his 02 cr 250. he went back to the original plug and it ran again. will keep you guys updated. also checked out the rc valve and it seems to be working properly, moving around a bit at idle then opening what seems to be full open with the throttle pinned

[dark6]

how is your air filter? I picked up a 02 cr250 guy said it was doing the same thing as yours got it home rode it yep fould out a plug..took a look at the air filter it was dirty and falling apart so i replaced it and the bike runs great all summer on one plug!

less air flow = rich.

[fordmugg]

Sometimes fouling plugs is just riding style ....my cousin would always foul plugs om his
02 cr250 because he rode to slow and the plug would build up ....I would ride it and itwoud b fine
Hope you figure it out

[kportingale]

so i put the different ngk spark plug back in. its the cheap br8es i believe and i got my top end power back but it still boggs bad at low rpm. not to sure what to try next, possibly leaking somewhere in the intake, chipped reeds, don't really know? don't think it's my riding style cause it ran fine for about 7 hours, now even when i put a brand new plug in it, it doesn't run properly right away even after takin it on the road and running WOT through all the gears

[MXtras]

Originally Posted by crguy

worn rings will not make it smoke more....

Well - this is not exactly true. Worn rings equal lower compression pressure which equals lower combustion temperatures which will equal incomplete combustion. So - worn rings will in fact cause a 2 stroke to run richer than a comparable engine with adequate compression.

Scott