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Old 12-13-2012, 07:28 AM   #16
stevemd OP
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Thanks Van. Tried some things after work yesterday: pilot out 3 turns vs 2. Gas cap loosened. Air filter pulled partially out to let some unfiltered air in (pool of filter oil in bottom of air box). No change worth noting, cannot back choke off more than %75 although as before starts easily hot or cold with choke full on.

Next step is more pilot adjustment in/out and if that doesn't do it, out comes the carb.

stevemd screwed with this post 12-13-2012 at 07:46 AM
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Old 12-13-2012, 10:23 AM   #17
MCCOYBOY
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Quote:
Originally Posted by stevemd View Post
Thanks Van. Tried some things after work yesterday: pilot out 3 turns vs 2. Gas cap loosened. Air filter pulled partially out to let some unfiltered air in (pool of filter oil in bottom of air box). No change worth noting, cannot back choke off more than %75 although as before starts easily hot or cold with choke full on.

Next step is more pilot adjustment in/out and if that doesn't do it, out comes the carb.
You have a blocked pilot jet. Pull the carb and either clean or replace the pilot jet. No response in pilot screw means no fuel flow through the pilot jet.
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Old 12-14-2012, 12:29 PM   #18
troidus
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Originally Posted by MCCOYBOY View Post
You have a blocked pilot jet. Pull the carb and either clean or replace the pilot jet. No response in pilot screw means no fuel flow through the pilot jet.
The jet may be clear, but the passageway clogged. Try blasting through the pilot jet with aerosol carb cleaner to see if you can get a good mist from the idle port and the transition port(s). Maybe alternate with compressed air from a blow-off nozzle, using a rubber tip for a good seal against the jet well. If blasting with cleaner doesn't do it, it'll be time for the ultrasonic bath. Pull off all your rubber parts before dunking it.

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Old 12-24-2012, 02:43 PM   #19
stevemd OP
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Update on this plus Season's Greetings:

Cleaned carb back in and looks like the pilot was clogged as will now run w/o choke after about 30 secs. Noticed that when I let it idle, rpms would rise for no apparent reason then come down a bit. Will try adjusting pilot screw.

Need to figure out if the multi-meter I have will read 1 cylinder rpms and where to take the readings off. Coil?

The Yamaha shop manual says to check the float level with the carb on the bike, bike upright, clear hose from the carb drain looped up alongside carb, measure how far fuel level in tube is from bowl/carb gasket. What a PITA.

Noticed there is a metal screen between the oiled foam air filter element and the carb. I would like to take it out to clean it but looks like the air box has to come out and I'm guessing the mono-shock has to be pulled to do that. Oh, well, a man's gotta do what a man's gotta do.

Thanks for advice to date and beyond.
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Old 02-09-2013, 10:10 PM   #20
someonesdaddy
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realize this post is over a month old, so i don't know what you figured out on this, but i picked up an 81 XT250 last weekend that had been not loved and not ridden for a good many years. carb was real cruddy and all honeyed up pretty good. pulled it apart and soaked it in carb dip on wednesday. pulled it from the dip yesterday, rinsed it in warm water and blew all the passages clean. everything absolutely clean and clear and all passages fully functional. ordered a Keyster rebuild kit for it and put it all back together today with a new float needle assembly (key note).

fired up second kick with the choke on full. did the same thing yours did, with the thing wanting to stall and not run without the choke on, and when i backed the choke off (before i reset the float) it idled high then stalled.

scratched my head for a second and remembered how the pilot jet did not sit that low in the fuel bowl, at least nowhere as near as the main jet - at least 10mm less if not more. knowing first hand that the passages/circuits were all clear i figured the fuel level in the bowl must be too low and the pilot jet was not submerged enough.

pulled the fuel bowl (carb still on the bike) and checked the fuel flow by opening the petcock and lowering the float slowly till the fuel started flowing. without having any factory specs in front of me, it looked like the float was probably set too low, so i bent the tang down a bit to allow a higher fuel level, put the bowl back on and sure nuff, the bike ran way better (went 55mph with no problem) without the choke on, but still wasn't real solid on idle regardless of any adjustments to the idle mixture screw.

after doing a little research on the web today, i found the float level to be 12.5mm +/- .5mm, so im gonna pull the carb again and set it on the bench to that spec. if its off (too high) when i pull it apart then that would explain a lot, and should remedy the problem.

moral of the story, your guy probably did a pretty good job rebuilding your carb but didn't set the float to the correct height, which would explain why your pilot circuit seems dead, unresponsive or way too lean.

let me know how it turns out on your bike.
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Old 05-10-2013, 08:09 PM   #21
GoO2
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Just picked up a xt250 . Did you guys find float height of 12.5mm right. Some old manual a friend had said 26.0mmm +-.5(top of float to gasket seat). Haven't dug into it yet.
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