Need Help with an XT250 Carb Air Screw Setting

I pulled my son's 1980 XT250 carb. down because it was running to rich. Thought maybe the air box needed opened up or the carb was dirty. What I found was the air/fuel screw was turned 8 turns out from seat. Anyone have an idea what it should be set for in Colorado? 2 or 3 turns out from seat? Thanks.


See ya on the trail.

I am pretty sure that the air/fuel screw you are referring to is usually set at 1.5 turns out. It actually regulates fuel delivery thru the idle circuit from the pilot jet. At high altitudes the setting may vary a turn.

One other place to look is the valve adjustments. If they are out of spec the bike will sem to run rich. Set the intake to .004" clearance and the exhaust at .006" for most Yams of that vintage.


I'm in Colorado (5280 feet) and run my '79 XR250's no turns out.

Yep, 1 1/2 to 2 turns out. While you have the carb out check the needle and nozzle for wear.

Check valves as aforementioned and also airfilter. A carboned up exhaust pipe on a high mileage machine can act a bit rich too.

Thanks OD I will look at setting the screw at the settings you suggested. I will also look at the valves. Thanks again.


See ya on the trail.

Hey OriginalDirt, talk about going from bad to worse. I got this XT250 back together and now it won't run without the choke on. Ideas? Very Lean? Here is what I did. It has a Uni-filter that was too big so I cut it down a re-oiled it. Cleaned the air box and opened it up a little with three 5/8" holes on the top, covered by screen of course. Cleaned the carb and reassembled, I don't like the way the acc. pump works but.... Set air/fuel screw at 2 turns out from seat. Now it will start good, runs okay at idel after it is warm, but will not open up past idle with the choke off. Acc. pump not working? Or is it just getting too much air now. Thoughts anyone. Thanks.


See ya on the trail.

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