dingoe

Member
Feb 13, 2003
291
0
Just picked up a YZ250 that was jetted for elevs of 2500 plus. Should be rich based on what I know, but when I road the bike at sea level if ran flat or boooowahed when I got on the pipe 1/3 to full. That would indicate it's jetted lean. How can a bike run fine at higher elevs jetted lean and not at sea level. I expected the bike to smoke and crack do to being rich. I haven't had time to go into it yet. Got home late last night, but I was thinking could the reeds hav cracks, or could it just need the clip moved down one notch. I have some work to do to get the bike to my liking and I'll run the choke test too.

Just wonder if anyone had any input, it's a 99 yz250 would be the same as the 2000 if your riding one of those. I ride everything from my home at 700' to racing in the high desert at 2500 to the mountains at 4500' I'd like to get it into that happy mid range jetting.

I'm in D37 souther california area.

Again the past ower said he had no problems at the races 2500-3000' or so and at sea lever it act lean. Just seems odd to me.


Guys I maybe mixed up on the lean vrs rich. High elev is low density so you do lean the jets. So I guess at low elev it would run flat. I'll pull the choke and if it runs better at the house than it is lean and should work better up high. I guess i can go to 50:1 or 60:1 from 40 or 32 to 1 and get it a bit rich would run better at 700-1200'. May wet foul the plug.

Thanks ed
 
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steve125

LIFETIME SPONSOR
Oct 19, 2000
1,252
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Yep you had it backwards at first. But now you see the bike has to be leaned for high elevations, and will be even leaner at sea level. That said put the jetting back to stock and adjust as needed. My advice is NOT to jet by oil mix, richer or leaner. On 250s I use 32:1 and 125's 20:1, with proper jetting, they never wet foul and run clean.
 

2strok4fun

Member
Apr 6, 2002
1,085
1
Ed,

I know I am jetted pretty close for the 2500 ft dez when it runs a *little* lean at my 400 ft ele at home.
 

dingoe

Member
Feb 13, 2003
291
0
Thanks for the input guys. The past owner was running 13oz to 5 gal or approx 50:1 lean premix that will richen his jetting. To me that says he has it set too lean from the get go. I'll adjust the jetting richer and run 40:1. I run 40:1 in the other bikes, a Polini works and a Planto Nationals race honda. They say run 50 or 60:1 in the Polini, but that's pushing it. If I put 40:1 in the yz now it will make the jetting even leaner. I'll try the clip position first and if not I'll go stock like Steve said and start from there.

I ride as much down here in San Diego and Riverside as I do up in Phelan and high dez, so it sounds like it will be an on going issue.

Thanks

Ed
 
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