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A cough and a sputter...

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Got an 87 Xr250r that starts first kick and runs mint until it warms up. When it's warm I can roll on the throttle and all seems well until I hit 1/4 throttle or so and then it breaks up bad. It will clear out though once I get to 3/4 and above. The engine is fresh, the carb is clean, and the bike is all stock. Could or does this sound like a bad stator? Or is my jetting just off? It has the stock jetting in it too. Any ideas??

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SoundS like a textbook case for a plugged pilot jet.

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Bike starts and idles fine. This is only when the bike is warmed up completely. It only breaks up in the midrange and can be cleared up by cracking the throttle WFO.

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The bike has stock jetting 125m, 40p, stock needle. The baffle is removed as well as snorkel. Uni air filter. So if anything she's running a tad lean. Why the break up in the midrange? It only does it when it's hot no other time. Someone told me a stator/cdi etc. might be the issue? Does that sound right?

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I would say no to ignition if it clears up WFO and I would say you are correct about the lean condition. I do not know XR400 jetting specs so I cannot comment on the correct jet size. A rich idle will mask an air leak between the carb and head up to about 1/4 throttle, as will WFO unless your main is marginally lean. Rule out ignition, rule out lean on main and what's left is pilot or an air leak between carb and head when you are talking 1/4 to 3/4 throttle.

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Why don't you check the needle position? The needle controls 1/4 to 3/4 throttle. Sounds like it's lean in that region. Move the clip DOWN to richen it.

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A 1996 and newer XR2.5 after Gordon's mods would use the stock 45 pilot and 135 main.

Most all fuel delivery issues on the XR's can be corrected with proper jetting also changing the needle clip position is more difficult than changing jets.

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