General Discussion Forum

the bike is a 2002 cr 250. It's a buddys bike and last time we went riding it ran fine all day. we get to my house and unload them. I hop on his bike to put it in the garage ( it's been cold for at lest 5 hours) start it rev it a few times to clean it out, and take alap around the yard to clean it all the way out. His bike always loads up pretty bad when you first start it and he normaly takes off down the road or holds it wide open till it cleans out, but i didn't want to blow his bike up or anything so i just do a lap around the yard and rev it a little, but didn't hold it till it cleans out, keeps running worse and worse till it finally chokes out and dies witha small backfire ( i think the backfire may be a key part in this)

 The whole time running was 1- 2 minutes at most.  Well I just thought i fouled the plug no biggie. Push it to the garage, tell him about it, a few days later he comes over puts a new plug in it, fires right up. But as soon as you give it more than half throttle it chokes out and wants to die, let off and it runns fine. If you hold it at more than half without letting off it'll die, it runs real good at part throttle though, compression si good and the powerband is there at part throttle, but as soon as you go past the certain point it'll imeddiatly bog out and want to die, it doesn't even TRY to run.

Thought it was a peice of dirtsucking up on the main jet when you opened it up, but tore the carb down and it was all clean. cleaned out all the jets anyways and it still does the same thing.

 Any ideas?

wow, its funny because when i read the title of the question i was thinking "sounds like the plug" but as i read the sotry i saw "my buddy came over and put a new one in" so next i thought "prolly the jetting" but i read more and see how you cleaned all the jets, honestly im some what stumped - i had the same problem and did everyhting you said and it seemed to work fine, im wondering if it might be the air filter? check how dirty it is and post a reply, or ask some of the veteran forumers such as ride cr or secondstringallstar

stupid hurts

i have an 02 CR250. i bought the bike down in the bay area. so thats what the guy had the bike jetted for. my first ride, the bike ran fine because the elevation was around sea level. but then i think my second or third ride, we went up to the mountains to do some trial riding. my bike had absolutely no top end at all. you would hold it wide open, and all it would do was bog, and if you held it long enough, it would almost bog out. i didnt hold it long enough to see if it would die though. the bottom was there, and most of the mid was strong too. so when we came back for lunch at the truck, me and my dad both decided to change out the main jet. all we did was drop the main jet and the bike ran beautifully on the after lunch ride.

so maybe this might help. i think the jet we have in there right now is a 380. im not sure, so dont hold me to it. i think the guy was running a 400 main at sea level when i got the bike. try dropping one main jet. and then after that check the plug to see if it is running too lean. if the plug is white, thats too lean. so there is my guess.

definitely not the jetting it's never been messed with and the bike has been ran at this elevation it's whole life.

could the small backfire have had something to so with it, like maybe the backfire cracked or broke the reeds? I'm probably going to try the plug again but he's put 2 new ones in it so i don't think thats it. Could it be something with the powervalve being so dirty from so much smoke when i loaded it all up? maybe the backfire messed up something with the powervalve? Ideas?

maybe the RC valve or whatever the valve is called that is on the left hand side of the cylinder, might be out of adjustment. your manual tells you how to adjust it. really i dont know exactly what is wrong with the bike. it is hard to pinpoint.

yeah try cleaing out the powervalve this is happeing to my freinds 03 CR125  

Its funny the ame thing happened to me this last weekend.  I also pulled out the carburater and cleaned it completely only to discover this was not the problem.  After a few hours of trying to fix it i took out my reed vavles and found out one of them was cracked, and on of them was sticking, once i put new reeds in it it ran fine.  I also had a buddy that this happened too and he put in a smaller main jet and it cleared his problem right up but that didn't work for me when i tryed it, i suggest checking your reeds.   

we're going to try messing with the rc valve and I'm going to check the reeds, they're the original ones that came int he bike so they're probably due, but it's still weird cause the bike ran perfectly fine all day until i fauled the plug and it had the little backfire.

i think its definitely the reeds. but if not the reeds or the powervalves, you should check your compression cause yz125 was doing something like that and i put in a new top end and it worked fine.  

Interesting problem.  Check the reeds for sure, that sounds to me like a damaged or broken reed.  The bad reeds I've had made my bike bog off idle though and start to clear up once I got into the mids.  They could have a funky crack or something not allowing them to open all the way.  Is the air filter clean and the air screw in the right setting?  Those sound like dumb questions, but usually a bog in the high RPM's is an air issue.  Is it just bogging, or is it making any type of clanking sounds near the front of the pipe?  If it is you might have a bad power valve that's not allowing the bike to exhaust properly.

Sorry, I was a little on the hammered side last night when I was writing replies   I forgot to ask if it was smoking when it's bogging.  It could be something as easy as having your mix way too rich.  Before you start ripping the bike apart, make sure thats not it.  Make sure the choke is working properly also.