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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
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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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Hi and welcome to Ninjette!!!

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
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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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Old March 15th, 2020, 01:45 PM   #11
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Update. Finally got around to this project. Cleaned the carbs 3 times (They were practically spotless to begin with) cleaned fuel tank, fresh fuel, and it was starting and idling great but falling all over itself in mid to high rpm....

It runs awesome when I block 2/3 of the air filter, I'd say better than ever before but any less than that and its no bueno.

Turns out stock jets can't keep up with the air flow.
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Old March 16th, 2020, 09:00 PM   #12
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Carbs are still not clean. I dyno-tested factory airbox, pods and zero filters (with full Tyga race exhaust). Exact same result with 96 mains (+22% more power than stock and still too rich at 11:1 AFR in high-end).
  • Did you use radioactive solvents in ultrasonic cleaner?
  • Floss out all fuel-circuits (not just jets) from beginning to end with scrub-brushes and guitar wire?
  • Follow up with soda-blasting @ 10000psi?

If not carbs aren't factory-fresh clean. Sure limiting air-flow to match clogged fuel-passages will balance out AFR, but that's not same as restoration to factory-fresh condition.

https://www.ninjette.org/forums/showthread.php?t=340561
https://www.ninjette.org/forums/showthread.php?t=339094
https://www.ninjette.org/forums/showthread.php?t=323737
https://www.ninjette.org/forums/showthread.php?t=323452
https://www.ninjette.org/forums/showthread.php?t=322846
https://www.ninjette.org/forums/showthread.php?t=321223
https://www.ninjette.org/forums/showthread.php?t=315193
https://www.ninjette.org/forums/showthread.php?t=317977
https://www.ninjette.org/forums/showpost.php?p=1225710

Quote:
Originally Posted by n4mwd View Post
Here are the secret passages in the carbs. They are kind of hard to figure out sometimes and this picture guide will show where they are for cleaning purposes.

Carb Pilot jet Circuit


Carb Main Jet Circuit


Carb Fuel and Overflow Drain


Carb Diaphragm Intake, upper choke and vacuum ports


Carb Choke Circuit
Also need to separate carbs to get to all nooks & crannies. And disassemble emulsion tube to poke out all bleed-holes with guitar wire of matching size.



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Old March 16th, 2020, 09:35 PM   #13
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@DannoXYZ

These pics are gold, thanks for doing that.
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Old March 17th, 2020, 06:06 AM   #14
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learning how to turn this into....this ....is helpful too

No mention of the decel valve, float system, setup, testing. Certainly more to it than poking with wires.

FWIW...not a fan of using guitar string (good luck with that) in any application other than the pilot jet orifice, alternate, efficient methods exist, though at a cost.
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Old March 17th, 2020, 11:27 AM   #15
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Yes, guitar wire very dangerous; needs lots of experience and musical ear to know which strings are of proper diameter. Softer copper wire is safer. Soft nylon brushes useful for fuel-circuits.

https://www.amazon.com/dp/B01N8SX03W

Mechanical removal of clogs from dried petrol is only method that works because spray carb-cleaners are now just weak carrier solvents that no longer have chlorinated compounds. Such as trichloroethylene, carbon tetrachloride, or chlorobenzene. Which provide real cutting power to break poly-vinyl bonds in dried-petrol clogs.

There are many, many folks who can re-build entire engine using just their teeth with both hands tied behind back who've had to pull carbs 4-5 times to do ever deeper and more thorough cleaning until it was factory-fresh clean. Or you can send them to ducatiman to get it done right 1st time!

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Old March 19th, 2020, 12:59 PM   #16
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Yes on the ultrasonic cleaner, I have no idea if its "radioactive", but i used a dedicated ultrasonic carb cleaner/concentrate.
No on the guitar string but I did use a carb cleaning wire tool set and brush kit.
Negative on soda blasting....
Yes on splitting. I was meticulous with each passage following as many different walkthroughs as I could find.
Yes on setting floats.
Yes on syncing carbs.

Just because bike "a" dyno tested with a particular configuration in no way means every other bike would perform the same...thats just silly....there's a lot of variables, the biggest unknown being who knows whats been done to this carb before I got it and including some outside of the bike itself (elevation above sea level) that play significant factor into fine tuning for a particular application.

Stepping up the jets tonight.
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Old March 19th, 2020, 03:44 PM   #17
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Entire group of Ninja 250 racers for past 12-years have developed configuration that makes maximum power, 22% more than stock. I personally know 15 that have gone before me suggesting exact same thing. Major sponsors have ponied up tonnes of money for hundreds of dyno-tests developing these bikes for racing. When Spears did mine, they didn't even need to do baseline test, they automatically threw in smaller 96-mains to save time on dyno-run that's been done before. Do you have:

- dyno-test with AFR curve?
- dyno-comparison of before and after of cleaning & mods?
- wideband plots of AFR over RPM?

Racers are cheating-bastards. If there's way to improve things, they'll find it to beat next guy. Fact that they've ALL arrived at exact same configuration across the country through independent testing really shows what actually works. Sure, larger jets to make up for clogged passages will work... only for while. You'll find performance slowly decreasing over time and will have to upsize yet again and again...
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Old March 20th, 2020, 07:33 AM   #18
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Question

What’s the best bang for your buck performance wise for the 250? I would like to be able to hit 100 to 105mph?

I have been experimenting with different rear sprockets, I tried 46, 45 and 43. With the 43 rear it doesn’t feel as buzzy but a little flat at certain rpms. I just have a slip on with a after market air filter (either a BMC or K&N I forget). My carbs can use a good cleaning, I will be sending them to Ductiman very soon.
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Old March 20th, 2020, 07:57 AM   #19
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Quote:
Originally Posted by JFMNINJA400 View Post
What’s the best bang for your buck performance wise for the 250? I would like to be able to hit 100 to 105mph?

I have been experimenting with different rear sprockets, I tried 46, 45 and 43. With the 43 rear it doesn’t feel as buzzy but a little flat at certain rpms. I just have a slip on with a after market air filter (either a BMC or K&N I forget). My carbs can use a good cleaning, I will be sending them to Ductiman very soon.
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Old March 20th, 2020, 08:48 AM   #20
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- dyno-test with AFR curve?
- dyno-comparison of before and after of cleaning & mods?
- wideband plots of AFR over RPM?

Nope, none of this is necessary, this is not a race bike. I will use what configuration works for this specific application without the unecessary expense of the above suggestions, hell a few dyno tests alone would eclipse the value of one of these bikes.

Again, there are substantiate variables that dictate optimum setup per engine...hell even per cylinder....compression, flow, timing, spark, vaccuum, climate, fuel, etc, making a blanket claim that if you do xyz you will get 22% more power is absurd speculation unless every single variable is matched.

This carb couldn't possibly get cleaner, and guess what...bumping the jets up worked fantastic. Is it possible that one of the other variables is responsible for this working in my application, sure....am I going going to chase those silly unknowns for absolutely no reason.....nope.
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Old March 21st, 2020, 08:42 AM   #21
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The tendency for humans to ask for advice, get excellent and correct advice, and then say, "nah, your wrong," and do their own incorrect thing anyway blows my mind.
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Old March 22nd, 2020, 02:33 PM   #22
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I never asked for advice on how to clean or tune a carb....i asked for jet vendors..thats it...

The tendency for every post on this forum carb related turning into hurrdurr send to ducatiman its the only way..is strong ....you cant possibly tune a 30 year old carb design on your own.

Runs stronger now than ever.
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Old March 23rd, 2020, 05:47 AM   #23
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Folks choose my service for various, very legit reasons.....lack of workspace, time, tools, equipment.

Well above and beyond "clean"....I refurb, setup properly and test, eliminating on and off "redo's".

Some of these bikes are ageing, demanding replacement of ALL "consumables", inspection and correction for ill advised "mods" performed by PO's (example giant, way oversized jetting), damaged threads, missing parts, poor adjustment....on and on many reasons.

A number of members offered up.....and in post #4 of this thread I offered you a source for jets.
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Old March 23rd, 2020, 09:45 AM   #24
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My mistake, you're in the other group that thinks they're right and never does figure out that they're actually wrong.
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Old March 23rd, 2020, 12:34 PM   #25
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ducatiman I don't doubt your expertise and appreciate the initial response in your thread above (I bought a few kits from them just be careful one of the jets I got wasn't even drilled through) and I'm sure you have many happy customers. I personally prefer to do my own maintanence, I've never subbed out work on any of my vehicles not even oil changes, so unless its machine work and I can't afford the machine tools myself, I'd prefer to build the skillset and knowledge myself.

Ralgha please clarify. Ask yourself what you are contributing here.

A new member joins this forum and asks a simple question and ends up being harassed by others making silly assumptions.

I knew exactly what this bike needed for my application. I only came to this forum for part vendors,not to be attacked by users that claim to know better than myself.

I always welcome knowledge of those with experience, I'm no stranger to sharing my own expertise but I sure as hell don't go around telling everyone they must do it my way or they are wrong.

I'm ashamed to be part of such an unwelcoming moto forum.

For others that find this thread and are looking for advice aside from paying others to do it for you:
$30 in jets and my own labor has this bike back on the road and running fantastic with the aftermarket parts I intended. No dyno, no custom tuner, no sodablasting, just patience, reading plugs, and progressive jet changes.....the same way its been done for decades.
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