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5 posts in this topic
By Matt Feldbauer
Hey guys so i have a pretty interesting scenario going on here. I got a used kx65 on craigslist that needed the bottom end rebuilt, couldn't really hear it run because the knock from the crank and bearings was so bad, so i replaced the crank, bearings, seals, and gaskets. (In my college apartment living room) Bike started in a few kicks! Here is where it gets interesting It starts up totally fine but anything past idle, it really spits and sputters, and past half throttle it wants to cut it out completely. I tried cleaning the carb once, checking the plug and it looks to be burning fine, adjusting the clip position on the needle jet up and down both ways, new gas. Could it be possible the top end would cause that? I did put the old piston in it but it didnt have much sign of wear, but I could be way off. Or is there some stuff I should try first again? Cleaning the carb again? Im open to any and all suggestions! Not willing to give up now, its so close to being done! I have rebuilt quite a few bikes now, 4 and 2 stroke so i have a decent amount of fix it know how, just really stumped on this.
I have a 2003 crf450r and when I got the bike it came with a white brothers carbin pro exhaust and was told it came from a 250f. The SS pipe mount between the muffler and header pipe does not line up without making a bracket but everything else fits.. The muffler mount ended up breaking and looking for a new one to put on now but bike specific ones are through the roof in price.
Does anyone know what 250f year might be the one I had so I know what to look for. Or any years compatible. 450/250 to a 2003 450f
I've read the page for compatible 450s saying 02/03 header the same and need full exhaust to run 03/04.
WOW, I have missed the community during the upgrade, but I am glad we are back up and running. I am in the process of replacing the top end on a YZ125 and going over my CRF250r and replacing all the items that need to be replaced.
Let's get back to the CRF. The right muffler had a big dent in the cone tip, enough that it was driving me crazy, so I bought a used one off Ebay to replace it. When I installed it, I noticed that the diameter of the hole was much smaller than the left muffler. The guy who sold it to me said it was pulled off an 07 CRF250r, just like my bike.
So, is the right muffler hole (at the end of the muffler) smaller than the left one? I just want to make sure I was sent the right one.
Here are some pics of the new one installed.
Just wanted to give you X fans some real world successful jetting settings. I just got back from a trip to Colorado and wanted to share these settings.
Our camp was at 6100' and we rode up to 13,000'. Temperature was between 65 and 85 (absolutely PERFECT!).
Airbox opened about a third of CCC recommendations.
Baffle removed, but spark arrester in place.
Pilot jet changed from 40 to 42.
-Needle in stock position
-Main jet - 142
-Air screw at stock position (I probably could have made some improvement, but I was having too much fun riding and I didn't experience any hesitation)
The bike ran great and climbed some HUGE hills. Most of our riding was single track, switchbacks, very difficult and technical - a lot of 1st and 2nd gear.
NOTE!! Apparently, the 250X is jetted lean in stock form. Opening the airbox and removing the baffle leans the carb even further. IF YOU DO THESE MODS, REJET YOUR CARB!!! Otherwise you could do serious damage to the motor. It will run significantly cooler when it is not lean. I live at about 600' and am running a 152 main jet.