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2001 DRZ400S cutting out in mid range

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I just picked up a 2001 DRZ400S with a few issues I've been working on. Engine runs good except for some hesitation in the mid range. When holding a constant 3K to 4K rpm in cruise, the engine feels like it is missing. I have gone through the carb with new JD jets, all new rubber bits and diaphrams. The bike had the 3x3 mod done already. Bike has plenty of power when you give it the trottle, but when you back off and hold a constant speed, it hesitates. I wouldn't think it would be electrical, since it runs good with full throttle. I'm going to change the spark plug just to eliminate that as a suspect. I just replaced a stator with low output and the battery charging seems to be back to normal. Should I go back through the carb again? I didn't soak the carb in cleaner, just sprayed some in the orifaces and rinsed it out with hot water. Any ideas? Thanks.

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Do you mean cruising about 1/4 throttle and your feeling a surge back and forth? If so try a 1/4 turn out on the fuel screw .

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Blue needle with circlip on the third position. 3x3 mod with JD jet kit. Using JD jet kit recommendations for jet sizes at sea level. Extended fuel mixture screw added. Stock exhaust and no engine mods that I am aware of. Is the fuel mixture screw responsible for the mid range performance? I though it was only for idle adjustment.

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Needle setting sounds ok, ... is a hot summer for you atm.?.If so it may be a tad rich... try running it without the air box side cover removed, run it under the exact same conditions and note any changes (if any)...if it's better in the mid range use red needle, clip 4...

 

Set your fuel screw/ pilot jet size using this procedure......http://www.thumperta...ad.php?t=327405

 

Have you only started having this issue since you replaced the stator?

Edited by Craig-o

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I live on the California coast in Santa Cruz on the Monterey Bay. Very mild weather here. Hardly ever gets over 80° F unless I travel inland 50 miles. It's been fairly cool this summer. I will try some airbox experiments like you and others have suggested, both with side cover removed and cover on with 3x3 intake taped up to 1x3.

 

I thought I adjusted my fuel screw using the proper procedure. It's at 2.5 turns out now. The bike still idled with the screw totally bottomed out and I didn't get real good definition of where the best idle was. I am wondering if that jet oriface has some gunk still in it. When I took the idle screw out the first time when rebuilding it, it was varnished up. I sprayed carb cleaner in the hole and rinsed it out with hot water, but I did not soak it in a bucket of carb cleaner or use compressed air to blow it out. When the needle is bottomed out I can see it protrude from the hole in the carb side opening.

 

The bike has had trouble with the mid range since my purchase. The stator replacement didn't seem to have any effect.

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