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03 450R breaking up between 5500-6000rpm

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So my 2003 CRF450R breaks up at 5500rpm and snaps right back to life at 6000rpm. Its all stock in the top end and has a plus 9oz flywheel and steel clutch basket. I swapped out the 172 main jet for a 175 and put in an adjustable fuel screw which seems to run best at 1 3/4 turns out. The pilot jet is stock. Valves are in spec and piston and rings are fresh. Any suggestions........

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It it rpm dependent or throttle position dependent?

 

If throttle position does not matter, it's probably electrical.

 

Try going through all connections, especially the coil ground and look for corrosion and bad insulation, replace the plug and re-install the plug cap after cutting off 1/2" of high tension lead.

Edited by Krannie

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It feels more throttle dependent, I just leaned out the fuel screw a bit and it seemed to break up a little sooner than 5500rpm which makes me think its running too lean. I wonder if all the extra rotating mass i added to the flywheel and clutch basket make it required more fuel?

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It feels more throttle dependent, I just leaned out the fuel screw a bit and it seemed to break up a little sooner than 5500rpm which makes me think its running too lean. I wonder if all the extra rotating mass i added to the flywheel and clutch basket make it required more fuel?

that would be weird, but try putting the screw back and raise the needle one spot. 

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