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Old June 28th, 2023, 07:11 PM   #1
truetaylorking93
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Exclamation 08 ninja 250 air filter mod problems

I have an 08 ninja 250. I did the air box removal and replaced with a kn r0990 filter pod with pod sock. Jetted carbs with 112. Used 2 needle shims. Bench synced carbs. Adjusted idle. I have done all new fluids, fuses, hoses, new carb, yoshimura slipon exhaust

Bike has to turn about five times or so before starting up then in every gear it runs to 7,000-8,000 RPMs tops. Max speed was about 57 mph
Factory I ran 100mph give or take and could redline. Now I can't redline at all while in gear

Someone said something about drilling out the fuel mix screws on the bottom and adjust those. Any info or direction would help. Thanks
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Old June 28th, 2023, 07:45 PM   #2
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Old June 28th, 2023, 07:50 PM   #3
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Welcome to the board, Clinton!

You have confirmed that removing the airbox causes all kinds of trouble and reduced performance that's hard to resolve. Making the idle screws accessible is a good thing, but the idle circuit won't do anything to help WOT mixture problems.
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Old June 29th, 2023, 12:11 AM   #4
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Put all stock jetting back into carbs.
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Old June 29th, 2023, 02:35 PM   #5
truetaylorking93
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To DannoXYZ

I tried to run stock carb after changing the air box mod. It did not work out good. The bike sounded like it was literally sucking air. I put the pod sock on and it came down a little. Way to much air to fuel ratio. Jetted the carbs then adjusted idle. Bike was clicking so I changed chain tensioner. That went away. Had a little leak on header. Changed header gasket. Checked valve clearance. It's good. Called Kawasaki today to verify (1) my bike doesn't have a fuel pump. It's gravity fed. (2) bike doesn't have a throttle position sensor. Kawi told me to check fuel mix screws and spark plugs
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Old June 29th, 2023, 04:48 PM   #6
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Something went wrong.

First, pods do not provide more air than stock airbox. Factory airbox and filtre are not restrictive in way. It's exact same size as on my CBR600RR. Bike which has 4x more power and 4x more air-flow. Racers have been using this bike for over 35-yrs and have amassed HUGE knowledge-base of what does and doesn't work. Racers are cheating bastards who will do anything and everything to get advantage over rest of field. Fact that pods are allowed in rules, and not a single racer amongst millions use them shows they don't provide any benefit.

My sponsor Spears dyno-tuned my bike in various configurations:

- factory airbox w/factory filtre
- factory airbox + K&N,
- pods
- no pods at all for most flow possible

ALL of mods provided exactly same power-output, about +1.5hp over stock. Meaning factory jetting is still way, way too rich. Here's '08 with K&N filtre installed in factory airbox:



Exhaust is where power can really be freed up. Full Tyga exhaust along with K&N got me +24% more power than stock. To get proper AFR, we had to decrease carb jets by 2 full sizes! And it was still slightly rich in 12:1 range. Decided to leave it at that since going to most-powerful 13.5:1 won't really give that much more power and best to have some safety margin in case I get bad petrol out in middle of boonies somewhere on super-hot day.

Something went wrong with your carbs during this parts-swapping process.
Put it all back to stock, including air-box and it'll run like before. However I bet it won't because something's not right. Vacuum-leak, missing or upside-down needle-jets, left/right needles got swapped, etc.

You want to make only one change at time so you can easily back up and troubleshoot:

1. replace ONLY filtre with K&N in stock airbox, how's dyno chart look?
2. replace ONLY factory airbox with pods, how's dyno chart look?
3. replace only main jets one size up, how's dyno chart look?
4. replace only main jets one size down, how's dyno chart look?
5. replace only main jets two size up, how's dyno chart look?
6. replace only main jets two size down, how's dyno chart look?

You need to take methodical and systematic approach with gathering and analysing objective quantitative data. Dyno is only way to gather those numbers.

Note super-rich factory WOT mixtures (left). Plugs looked like this after 20-minute session on track. Plugs were actually black, flash lightened everything up.



Adding full-exhaust, DynoJet leaning needles, downsizing 2 main-jet sizes got me mixtures on right set of plugs. Along with +24% more power and top-speed increased from actual 97-mph to 110mph (GPS + calibrated TrailTech Vapor dash @ Thunderhill Raceway).

Note DynoJet needle (bottom) is fatter in high-end compared to stock in order to reduce super-rich WOT high-end mixtures. Also slightly slimmer in mid-range to fix lean-spot (6-7K-rpms in above chart).



What you need to do is look at numbers. I've highlighted important numbers in bold to show cause & effect relationships. Here's only ones you've gathered:

98 main jets = 100mph top-speed
112 main jets = 57mph top-speed

So what logical cause & effect conclusion can you deduce from these numbers ??? As in which configuration gives you higher top-speed? Another logical deduction is: Which configuration gives you more power???



Some related reading:

'08 Ninja 250: Racing On The Cheap - SportRider scroll down to Nuts & Bolts section
Dyno Testing - +22.5% more power on stock jetting! Lean only in mid-range and thinned needle to correct (BTW - RacerX got 123mph from Ninja 250)
Racing Order - Dyno testing - 32.3hp (+22%) with just the Tyga exhaust, snorkel removed and stock jetting.

Last futzed with by DannoXYZ; June 29th, 2023 at 06:28 PM.
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Old June 29th, 2023, 07:53 PM   #7
truetaylorking93
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To DannoXYZ

I believe that might be my problem. The jet kit I received didn't come with new needles. Only jets and spacers. So I'm running with different jets but factory needles
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Old June 29th, 2023, 10:39 PM   #8
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From those jet sizes, you got kit for pre-gen '88-07.

You want Dynojet kit #2193 for '08-12 new-gen.
https://www.dynojet.com/jet-kit-for-...0r-ex250-2193/

Start with mains # DJ100 which is similar to Keihin 102. Do dyno run.
Then use next size down DJ98 and do another dyno run.
You'll find best power with DJ94
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Old June 30th, 2023, 01:24 PM   #9
truetaylorking93
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Can you run jet kit with factory needles. If so how do you do it or what's the set up. Jet kit didn't include needle that can be adjusted. My bike comes factory with a needle that can't be adjusted. What do I need to do
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Old June 30th, 2023, 02:14 PM   #10
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Traditionally, "jet kits" have always included adjustable needles. As you've ordered an incorrect "jet kit" without needles...I'd suggest replacing same with a Dynojet kit Stage 3 #2393 for starters, and be prepared ....further tuning will no doubt be required to achieve sufficient running status, from idle through all throttle openings.

Yes, removing the EPA anti-tamper caps covering your pilot screws (thus enabling removal, cleaning AND RE-SETTING of same) is a critical component to both basic carb cleaning AND tuning setup.

DYNOJET 2393 KIT INCLUDES:
2 Main Jets DJ104
2 Main Jets DJ108
2 Main Jets DJ112
2 Main Jets DJ116
2 Fuel Needles DNO308
2 Slide Springs DSP031
2 E-clips DE0001
4 Adjusting Washers DW0001
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Last futzed with by ducatiman; June 30th, 2023 at 05:23 PM.
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Old June 30th, 2023, 02:40 PM   #11
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DYNOJET KIT 2193 NOTES:

For mildly tuned machines using the stock airbox,
with the intake snorkle removed and stock or
K&N filter. May also be used with a good
aftermarket exhaust system

DYNOJET KIT 2393 NOTES:

2393.001
U.S Models Only
2008-2012 Kawasaki
250R Ninja
Stage 3
For mildly tuned machines with the stock airbox
removed and K&N filters installed.
May also be
used with a good aftermarket exhaust system.
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Old June 30th, 2023, 02:45 PM   #12
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Based on your choices....the rest is up to you.

Good luck.
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Old June 30th, 2023, 04:47 PM   #13
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I recommend reviewing Scientific Method. It is process used in pretty much all engineering and research & development projects. Note important step is gathering empirical objective data and analysing that data to see if results are what you anticipated. Then formulating new plan to steer project towards your goal.

Read these texts on internal-combustion engine theory and tuning. Basically 1st-year FSAE background stuff before we got hands dirty with actual engines. I have all these on bookcase, can loan them to you with deposit. Best stuff I've ever learned.

Internal Combustion Engine Fundamentals - Heywood 1988 McGraw-Hill
Engineering Fundamentals of Internal Combustion Engine - Pulkrabek 2003 Prentice Hall
Flow and Combustion in Reciprocating Engines - Springer, Arcoumanis, Kaminoto 2009 Verlag Berlin Heideberg
Performance Tuning Theory & Practice - Four Strokes - Bell 1981 Haynes
Tune & Modify Automotive Engine Management Systems - Hartman 2004 MBI Publishing
Motorcycle Fuel Injection Handbook - Adam Wade (click for freebie chapter).

Thing is... you don't have to re-invent the wheel. Millions of racers have taken this path before you since 1986 and done exact same trial & error process. All you have to do is look at their results and replicate their steps. I got my 250 up to 110mph top-speed (122 on dash). Racer_X got his Bonneville bike up to real 123mph (136 on dash). You'll want to examine experimental data and results of anyone you're talking with about upgrades. Do they have measurable results you're looking for?.

Heck, Spears was one of original racers of these bikes back in 1988 and is more knowledgeable than anyone I've encountred. And I've met at least 100 racers who've modified these things extensively with engine-boring upgrades, casting their own engine-blocks, along with EFI conversion, nitrous/methanol injection and turbocharging!
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Old July 1st, 2023, 02:19 AM   #14
truetaylorking93
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To ducatiman

Would rejetting and tuning fix my problem with not being able to redline??
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Old July 1st, 2023, 05:44 AM   #15
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Of course..... provided your engine is up to spec, (not been modded/tuned/destroyed/damaged out of function) and also provided you hit the correct carb setup.
The process may likely require many carb removals/jet changes/experimentation until the correct setup is discovered.

Another alternative....return ALL (airbox included) back to known stock/factory spec/setup.
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Old July 1st, 2023, 02:27 PM   #16
truetaylorking93
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Thank you all for replying and trying to help me. Looks like I will probably be going back to stock. I feel like I'm wasting money for the outcome I'm going to have
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Old July 5th, 2023, 08:51 AM   #17
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I'd say go back to the stock airbox and use the data Danno provided to get your jetting optimized.

Know that the jet numbers on Dynojet kits are proprietary, and do not match factory Kehin numbers. Factory Pro jet kits use correctly numbered jets. Many eBay no-name kits are way off, and should be avoided.

Pods just don't work well on most bikes, and often create a flat spot, poor throttle response, and low torque at lower RPMs that can't be tuned out.

Some engines, depending on the size and design of the airbox, may pick up some power at the very top of the RPM range - but everything else usually suffers.
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Old July 5th, 2023, 09:47 AM   #18
truetaylorking93
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Thank you for bringing that up. I did not know that about the jets being different. Here is the chart if anyone needs to cross factory jet numbers to dyno
Attached Images
File Type: jpg Screenshot_20230705-114121.jpg (63.4 KB, 4 views)
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