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Old July 16th, 2022, 05:04 PM   #1
Fatherof2
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Name: David
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Motorcycle(s): 2017 Triumph Trophy, 2001 Honda Valkyrie, 2007 Ninja 250, 2017 Yamaha 250X, 2018 YZ125

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Slight hanging idle question.

Hi Gang,

I picked up a 2007 250 with less than 3K miles. It had been sitting for a long time.

I rebuilt the carbs, and the bike starts easily. It will start without choke on these warm days we have been having.

When the bike is idling at 1500 rpms, and I blip it up to 3,000 or so, the idle hangs up there a bit and kind of slowly drops back down to 1,500. It feels like a delayed reaction as it returns to 1500ish.

If I rev it up to 4 or 5K and let it drop back to 3Kish, it seems to come back down in a more normal fashion.

Bike screams nicely when up in the higher rev range. Seems to be running fine when I do that.

Any input is appreciated.

Thanks All!
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Old July 16th, 2022, 05:37 PM   #2
DannoXYZ
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MOTY - 2018, MOTM - Nov '17
1. Did you disassemble down to every last nut, bolt and individual component? If it can be further disassembled, do it.


2. Poked out all lateral bleed holes in carb-venturi, emulsion-tubes, pilot-jets?


3. scrubbed out all secret hidden passages with PEA-based fuel-system cleaner with brushes?
http://n4mwd.blogspot.com/2013/10/se...-passages.html

4. ultrasonic soak, micro soda-blast everything?

5. replaced all rubbers: fuel-rail O-rings, float valves, mixture-screw O-rings, float-bowl seals?

6. set float-height with final wet-test to verify?

7. sync carbs after installation?


Do search on here for "clean carbs ducatiman" for threads with how-tos and photos.
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Old July 18th, 2022, 07:25 AM   #3
jkv45
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MOTM - Jun '18, Oct '16
Danno pretty much has it covered. Doing carbs right isn't quick or easy.

Many times, hanging RPMs means a vacuum leak -but it can also be just a lean condition due to improper adjustments or partially plugged carb circuits.

Did you remove the idle mixture caps, idle mixture screws, clean the passages, and check that the o-rings are in good condition?

Most of the time, when everything else is correct, setting the idle mixture screws to 2-turns out initially gives you a good place to start.

After it's fully warm, I will adjust the screws to get the highest RPMs at idle, go about 1/8-turn out (richer), then set the idle speed to 1200 or so.

Syncing the carbs is also a good idea before fine-tuning the mixture screws.
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