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JLB943

03 YZ450 Just Not Runnin Right

4 posts in this topic

I have an 03 yz450 that I have had for awhile now. I put an old style rekluse z-start clutch on it and have rode it alot. It was fine but now it just seems like the power is not there on the bottom end. It wants to rev really slow. I put the an air fuel mixture screw with the knob on it and played with that. I had a 13oz flywheel weight on the bike before I put the auto clutch on it. I am wondering if I should remove this because the clutch has added extra mass and it is reving really slow. I pulled the jets and they look clean. The other problem that sometimes when the throttle is chopped and then I get back into it real quick it stalls. I believe this is the clutch. I just want the snap back that it had, when I get into the throttle it jumps to life. I have been riding alot of mx tracks and when I get into coming it a jump feels like I am waitng for the power. Any suggestions?

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I've had good luck with the aluminum air screws, but I've read bad things about them. You might try putting the stocker back in for testing. most people remove their flywheel weight when going to the rekluse , but it sounds like you had both for a while and were happy, but now it's having issues? If you're concerned it has something to do with the rekluse, just put the stock bits back in test it.

Is there anything you can add? This just started all of a sudden? The back hadn't been sitting? No work was performed between the last good ride and how it rides now? Was this a degradation thing, or just happened one day?

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The stalling issue is either due to the clutch being set up to engage too suddenly, or from too rich an idle mixture. Tyr setting the idle up according to these guidelines:

http://www.thumperfaq.com/jetting.htm#PJ

Then read this info:

http://www.thumpertalk.com/forum/showthread.php?t=327405

Added clutch weight has almost no effect on the engine revving because the clutch turns at less than a 1/3 the speed of the crank, and has to deliver any rotating inertia to the crank through a 3:1 disadvantage. Your power problem will turn out to be cam timing, or an ignition or carb main circuit problem.

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Greyracer,

Based on that information with I am less than one turn and believe I may have to go smaller on the pilot jet. I am less than one turn out I believe. I am going to get a size smaller pilot jet and try that.

The clutch engagement seems ok. It does want to keep driving when I brake to a stop. If I push on the acuator arm slighlty it stops so I have been working to get the tension and adjustment right so it does not want to keep going. I am close to going back to a regular clutch but I had issues with stalling alot with the regular clutch and thus tried the auto clutch.

I will do some searches to see what the best jetting people ended up with for an 03 450. I believe the main jet is currently a 164 or 165. I don't remember what the pilot was.

The power being down off idle may have been going on for awhile I just haven't noticed it. I have been riding alot more, got my suspension tuned and have grown more confident. As a result, I am getting on it into jumps where before I was not.

How would I go about checking the ignition and cam timing? I have to check the valves soon so this would be a good time to verify this is correct.

I went to look at a 2011 yz450 last friday, I think my bike got wind of it and decided to start acting up. :)

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