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2003 CR250 intermittent issues

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Alright so I recently bought a 2003 cr250. The bike is really clean for its year if you ask me and I got a great deal considering I live in New England and everyone now wants one.

 

So anyways, the bike is basically all stock besides a Pro Circuit pipe and R-304 shorty. It was running rich down low so I messed with he jetting. It had stock jetting (30 pilot, 420 main, needle in 2nd clip from the top,and air screw 1.5 turns out). I thought it was odd that it had a pipe on it and was still running rich down low. So I dropped the needle to the lowest position (top slot) and it ran a lot better. Still not perfect tho. So I backed the air screw out in 1/2 turn increments until I reached 2.5 turns out and had it running pretty decent. Then I picked up a 27.5 pilot and tossed that in and I basically have the bike running perfect. Plug looks like its burning really well and has great throttle response compared to when I first bought it.

 

I have this intermittent issue that is sorta hard to explain. After about an hour of engine time or so (motors at operating temp) the exhaust will get really loud as if the shorty is falling off. The pipe makes a loud "ping" at every stroke of the motor as if its straight piped. Again, its kinda hard to explain. But he bike will also run poorly and bogs and hiccups for a few seconds (WOT) until it will open up and then it screams. As soon as I let off the throttle and let the rpms drop down to anywhere from low to mid range it will do it again. Pipe sounds loud, runs horrible, ect. I've found that the bike seems fine if I let it fully cool down or ride it again the following day. My guess is it is getting a weak spark intermittently but I'm not 100% positive and would like some advise from you guys.

 

Sorry about the novel, I'm just tying to explain everything as best I can so it may be easier for everyone to understand.

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Is it burning tranny oil do you notice not as much comes out as goes in? Seems awfully lean in pilot jet . 

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IMG_3763.thumb.JPG.45215e4e076cb921c878560b1ac2f596.JPG

Here's a pic of the plug that was removed as it was acting up. The plug only has a few hours on it.

IMG_3768.thumb.JPG.43384ea257e63d4eae74ba7b99fa4942.JPG

 

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Ya looks pretty good. Possibly stator going south maybe.  Something getting warm and then your problem occurs from what I read . Usually stator related or crank bearings sloppy and worse when warm. Gas cap vent maybe.  Try little things first never know.  Floats in carb but runs good for awhile you say so doubt it's carb retated unless petcock it plugged or something like that

Edited by Motox367

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Ya looks pretty good. Possibly stator going south maybe.  Something getting warm and then your problem occurs from what I read . Usually stator related or crank bearings sloppy and worse when warm. Gas cap vent maybe.  Try little things first never know.  Floats in carb but runs good for awhile you say so doubt it's carb retated unless petcock it plugged or something like that

I've set the float height to spec before I messed with the jetting. Sorry I forgot to mention that. I don't think it's the tank vent but I will have to take it out riding today and see if it does it again and open the tank. I'm going to strip the plastics off the bike and look for any obvious signs of wiring issues or anything of that matter. If it is the coil or stator, I don't under stand why it doesn't do it as soon at the motor warms up. Like 10 minutes or so. Instead it takes about an hour

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4 minutes ago, Mike Daley said:


I've set the float height to spec before I messed with the jetting. Sorry I forgot to mention that. I don't think it's the tank vent but I will have to take it out riding today and see if it does it again and open the tank. I'm going to strip the plastics off the bike and look for any obvious signs of wiring issues or anything of that matter. If it is the coil or stator, I don't under stand why it doesn't do it as soon at the motor warms up. Like 10 minutes or so. Instead it takes about an hour

Ya that's the odd part. Hopefully you figure out :thumbsup: hard to help from other end of phone lol

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Yeah I don't understand. I might throw a coil at it if I can't figure it out soon to see if that helps. I'll report back if I find anything once I tear it apart

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My money is on a sticking power valve! My bike did the same thing.. The power valve would stick open and the bike would suddenly get VERY LOUD.. Also, when the power valve sticks open the bike will have poor low end performance and won't want to build RPM, or rev out, very fast. You will have to wait until the RPM's get up there a little bit and then it feel normal.  Since you indicate this is an intermittent problem, it also points to a sticky power valve.

If you have not inspected the power valve lately, or ever???, maybe it's time to pull it apart and clean it. The Factory Service Manual calls for removing & cleaning the power valve assembly on a frequent basis. I can't remember the exact number of hours the manual calls for but I think it was something crazy like every 10 hours or so. I know most (any?) of us don't do it that frequently so if it has not been done in a few years on your bike it might be the first place to look. Mine DEFINITELY was the power valve as once I disassembled the head and got everything out on the bench you could see the baked on carbon on all of the parts. It was NOT easy getting all of that crud off those parts but once I put it back together-no more obnoxious noise, no more sputtering on the bottom end. Problem-for me-solved.

Hopefully this is all that is wrong with your bike. I will go on to say that mine only gummed up after using Castor bean oil (927). It NEVER before gummed up, and never since. I now ONLY use Lucas Semi-synthetic.

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