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Old January 13th, 2020, 11:48 AM   #1
shaverjeff
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New Ninja - where to get main Jets

Picked up a 2008 stock 250 for the wife to start learning on.
It sat for a long time so I cleaned carbs and switched to a pod filter (K&N style) to avoid future airbox hassles. Planning on a slip on exhaust too but I'm having trouble finding a main jet kit. It looks like I likely want a 110 main jetbut most of what Im finding has very poor reviews and I'd like to avoid buying a complete carb kit if only the main jet is required.

Can anyone point me in the right direction?

I ended up making a simple bracket to hold on the filter as the clamps didn't seem enough, I cut the stock metal screen to act as a large washer. Much easier to access carbs now.

https://photos.google.com/share/AF1Q...1hZFVOODRoNUpn

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Old January 13th, 2020, 12:12 PM   #2
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What's in it now?

We ran 108s with pod filters and a leaky stock exhaust on out PreGen and it was plenty rich on top.
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Old January 13th, 2020, 12:15 PM   #3
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No exhaust upgrades? That’s where monster power is unleashed (+22%).

With that filter, you’ll gain minimal extra flow. Most intake restriction is not in airbox or filter, but rather in tiny intake ports and mild cam specs. That’s why they went to 98 mains in new-gen from 105 in pre-gens. Largest you’ll want is 96 main, since that will still be too much fuel up top, +15-20% too much.

Search for “clean carbs ducatiman” to see why upsizing jets is mistaken step.
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Old January 13th, 2020, 12:26 PM   #4
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www.jetsrus.com a good source for your needs
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Old January 13th, 2020, 12:42 PM   #5
shaverjeff
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Thanks for the replies. This filter upgrade was initially just to make access easier, because the bike sits for long periods I was getting bored of fighting the airbox, I'm planning an exhaust too, nothing fancy though just something that makes it easier for the wife to hear.

Current jets are whatever came stock the bike only has about 600 miles on it since I picked it up last year. In current form with the new filter and stock exhaust (which will be replaced) its extremely boggy down low but seems to run better in the higher rpm range. It fires right up, but takes several minutes before its responsive, and even then down low rpm like below 5k is really rough.
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Old January 13th, 2020, 01:12 PM   #6
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Quote:
Originally Posted by shaverjeff View Post
its extremely boggy down low but seems to run better in the higher rpm range. It fires right up, but takes several minutes before its responsive, and even then down low rpm like below 5k is really rough.
We’ve all had this issue before. If it’s sat for more than 3-months, you definitely have clogged carbs that needs thorough cleaning to restore to factory fresh condition. Bike ran perfectly when it left showroom floor, and there’s no reason it can’t again with all-factory jetting (even better with downsized main jets).

Behavior down low has nothing to do with main jets. That’s all in choke and pilot circuits. Here’s various areas of adjustments in carbs and which corresponding operating zones they affect.



Low end behavior with warm-up, idle and low-RPM operation is all controlled by choke, pilot-jet and pilot-screw adjustment. And they need cleaning and adjustment, not upsizing. I’d say you need thorough carb cleaning, especially pilot circuit. Spray cleaners no longer work due to removal of chlorinated compounds. You’ll need lots of scrub brushes, guitar wire of various gauges, ultrasonic cleaner with caustic radioactive solvents, micro soda-blaster @10000psi and lots of previous practice to use them effectively. Search for “clean carbs ducatiman” for cause of this low-end issue and how to fix it.

Here’s dyno-chart of factory 250. You can see AFR in high-end is way, way too rich. Adding more fuel there with larger main jets will do no good. Can even damage engine as extra fuel will wash oil off cylinder walls and cause accelerated wear.


Last futzed with by DannoXYZ; January 13th, 2020 at 02:51 PM.
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Old January 13th, 2020, 02:49 PM   #7
shaverjeff
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thanks DannoXYZ you likely saved my buying something I don't need.
I'll have a go at cleaning them on my end, worse case I'll drop them off at a nearby shop.
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Old January 13th, 2020, 03:03 PM   #8
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Quote:
Originally Posted by shaverjeff View Post
thanks DannoXYZ you likely saved my buying something I don't need.
I'll have a go at cleaning them on my end, worse case I'll drop them off at a nearby shop.
I wouldn't do that. It's rare that you are going to find a shop that really knows how to clean and adjust carbs properly.

If you need them done professionally, contact ducatiman (posted above).
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Old January 13th, 2020, 04:30 PM   #9
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Quote:
Originally Posted by shaverjeff View Post
thanks DannoXYZ you likely saved my buying something I don't need.
I'll have a go at cleaning them on my end, worse case I'll drop them off at a nearby shop.
Heh, heh... last time I did that many, many years ago with my 1st 250, I got call back three days later: "We can't figure out how to connect OBD scanner!"
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Old January 20th, 2020, 11:57 PM   #10
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Quote:
Originally Posted by DannoXYZ View Post
Heh, heh... last time I did that many, many years ago with my 1st 250, I got call back three days later: "We can't figure out how to connect OBD scanner!"
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