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Colorado YZ 250 jetting at altitude

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Just picked up a non running 92 YZ 250. Owner said it overheated last time he rode it and then it sat for a year. Was hoping someone could give me some thoughts on jetting. Colo Spgs is 6200 ft altitude and we usually ride between 6500-9000 ft altitude. Current specs are as follows:

Mikuni 38TM flat slide carb

Stock needle with clip one notch higher than center

Pilot jet is a 45, stock is 50

Main jet is a 300, stock is 350

I think the main jet is a little too small and maybe this contributed to the overheating. I was thinking a 310 or 320 once I get it running again. I have looked through tons of forums and the local shop wasn't much help, any thoughts are appreciated

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If I were to start jetting it from scratch, I would leave the stock pilot in and the main 3 sizes less than stock, so a 330 main. It needs about half a needle clip leaner. If you had a .020 needle shim on the stock clip, that would work great.

 

The reason for the stock pilot is that the vacuum signal generated with thin air pulls less fuel through a given jet, so the 50 pilot will flow less at altitude. Run 3 ounces of oil per gallon for trail riding. That's 42.6 to 1, and an easy number to remember.

Edited by Leardriver

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