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Old July 29th, 2020, 07:51 PM   #1
Shenal
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2008 ninja 250 jetting

hey guys, ive had my ninja for 2 years now. Ill have to keep it for 2-3 years before i can get a faster bike so i have been playing with the idea of doing a jet kit to get a little more power and response out of the bike. So far my bike is pretty stock. It has 30000k on it and all i have is a slip on exhaust. I was wondering which stage dyno jet would work best for me? i dont mind deleting my air box and snorkle and getting a k&n 0990 filter. I have seen on fortnine that they sell a stage 3 dyno jet kit and stage 2 for a reasonable price. Maybe i should just go to a Kawi dealer and get larger main and pilot jets? Any help would be appreciated. thanks!
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Old July 29th, 2020, 08:06 PM   #2
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Old July 30th, 2020, 10:59 AM   #3
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Old July 30th, 2020, 02:29 PM   #4
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Larger jets will only hurt your performance, as will deleting the airbox, it flows plenty of air for the bike. Removing the snorkel certainly won't hurt, but it's debatable as to whether it really helps at all. Your slip-on is also doing nothing for you.

Easiest way to get more power is to clean the carbs.

Assuming the carbs are clean, then get more power by installing a full exhaust and then tuning the carbs for that. You will probably need smaller main jets, not larger ones. That should put you in the 30HP ballpark.

After that, you're getting into things like boring out the cylinders and stuff.
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Old July 30th, 2020, 02:59 PM   #5
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Thing to realise is that what generates power, is oxygen. It burns with petrol in 14.7:1 ratio for maximum BMEP (cylinder pressure). Any more or any less than that and you don't get complete combustion. But, in practice, it's 13.5:1 AFR that yields most power with some extra fuel to ensure that all oxygen molecules are burnt.

Thing is, fuel is easy because it's required in much smaller amounts than oxygen. From factory, these bikes run super-rich in WOT/upper-RPMs, something like 10.0:1 AFR which is maximum 5-gas analysers can record on dyno. So most likely it's even richer than that! Every single bike I've ever dyno-tested, over 30 different models, have always been too rich. So... to make more power, you just remove fuel and add oxygen. Remember that '60s hot-rod saying, it's still as true today as it was back then.

Tough part is getting more air/oxygen into engine. Intake side is perfecty fine without porting head and installing larger valves. Exhaust is really only place that can be improved and that requires full-exhaust. Ideally design that doesn't poke into and narrow exhaust ports, but no one makes an off-the-shelf item like that. At least full-exhaust will get you most improvement possible on this bike.

After that to increase air-flow and more oxygen into cylinders, you gotta put in bigger pistons and valves.

More fuel without increasing air-flow will just lower your power.
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Old July 30th, 2020, 06:04 PM   #6
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I have thought about this a lot and did some research.

Air boxes have a very important job, it is to stabilize the air coming into the motor. Think about how chaotic it is inside each cylinder during each of the 4 strokes (suck, squeeze, bang, blow) and consider how hard it is for the motor to pull in a consistent volume of air to fill the cylinder. Throwing on pod filters on a drag bike makes a bit more sense because generally you are removing most of the fairings on really high end fast stuff. The speed of the bike makes it easy to fill that volume.

Consider your bike just putting around town, maybe on the highway, all the fairings on. How much air is actually getting to those pod filters? The general idea people have is "I want to give the air the most direct path to the carbs/throttle bodies.

Looking at MotoGP bikes, which most people consider the gold standard in the sport bike world, they do very little modifications to the air box and usually run the factory one.

These Things are designed using 3D CAD software with flow charts, ran on dyno's with several different variations, and tuned to ensure the most stable intake air volume is achieved.

When you see video's of people who say they cut the snorkel off, not to rag on anyone who has done it, but generally they have done a LOT of modification because the bike is already apart. ECU flash, air filter, jet kits, chain/sproket, 3/4 throttle, etc. At the end of it they bring up cutting the air box or removing it in some way, shape, or form.

If you REALLY want to know if mods are actually going to get you the performance you want from the bike I'd take Danno's advice he gave me.

BUY A WIDE BAND O2 SENSOR AND BRING IT TO THE DYNO.
This will net you hard and concrete evidence as to what the mod actually did to the bike, actually did to the AFR. Sure it is expensive but in the end you might end up spending a lot more money have have a bunch of parts sitting around you uninstall and are unhappy with.

Edit: I came across this channel called "The Workshop" and I am gonna keep pushing it for everyone to watch and learn from because the knowledge the guy has is extremely practical and super easy to follow. He is an engineer who LOVES bikes, loves every aspect of bikes, but hates stupid bs people say but can't back up with actual real and quantifiable numbers.
Here is a link to a great video on this topic. https://www.youtube.com/watch?v=_vE0EwYiE4U
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Old July 30th, 2020, 11:52 PM   #7
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Now there's some truth to this "automatically rip out airbox and install pods with giant jets" idea. It really had to do with early days of sport bikes way back in '60s before age of computers and CFD software. With Honda's breakthrough CB750, suddenly bikes took a huge jump in displacement and engine size. None of manufacturers had built anything so monstrous before and there was no database of engineering data on how to build huge bike engines.

And being short on time with insufficient R&D, they just scrambled to get a big bike out to market to compete with Honda. Result was lots of bigger bike engines were built with of-the-shelf small-bike parts in haste. You ended up with tiny carbs and airboxes being grafted onto engines much larger than they were originally designed for.

So of course this new generation of big bkes ran poorly in factory trim. Tuners and aftermarket suppliers came up with ways to unchoke these monster machines being forced to breath through straws. So yes, on big 750-1500cc machines breathing through shoebox-sized airboxes and sandwich-sized air-filters, removing them and giving each carb their own filters does improve breathing and gets more air into engine and more petrol is needed.

However, by the '80s, bike makers had figured out how to match airboxes, filters and carbs to engine-sizes. CV carbs became extremely precise mechanical computers that can meter exact amounts of petrol needed in large variety of operating conditions from idle all way to WOT @ redline. Pretty much any bike from '80s onwards has no need in factory trim for any changes to intake system.

Tuners still had ways to improve on factory designs because they're not constrained by needing 100k-mile durability, cheap manufacturing or emission regulations. So as with autos decades earlier, factory engines were ripped apart and larger higher compression pistons were installed. On one particular EX500 engine I saw, there was enough room between new big-bore cylinders and factory pistons to fit an entire finger through! They had bored out EX500 engine to 600cc! So of course intake needed more breathing than factory airbox and fi!ter allowed. And custom cams and custom spun valves were needed to flow that extra air. So jet-kits were designed with these kinds of air-flow increasing mods in mind.

Check out Bruce's, Garth285 and RacerX's builds for flow-improving mods. Big-bore pistons and turbos increase amount of oxygen going into engine and jet-kits are way to match petrol-flow to new air-flow patterns. Yeah, A LOT of dyno-tuning time is required to dial in these beasts with double factory air-flow and double power! Note that tuning with jet-kits come after air-flow increasing mods. It's mods that come first, and tuning with jet-kits is done as last step to tie all previous mods together.

Wth modern computer-designed engines and dyno-tuned carbs, there's really no simple way to improve them. But decades-old tuning ideas still hang around.
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Old July 31st, 2020, 08:52 AM   #8
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Quote:
Originally Posted by Emu View Post

Edit: I came across this channel called "The Workshop" and I am gonna keep pushing it for everyone to watch and learn from because the knowledge the guy has is extremely practical and super easy to follow. He is an engineer who LOVES bikes, loves every aspect of bikes, but hates stupid bs people say but can't back up with actual real and quantifiable numbers.
Here is a link to a great video on this topic. https://www.youtube.com/watch?v=_vE0EwYiE4U
I watched this video and loved it. Thanks for sharing.
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Old July 31st, 2020, 11:29 AM   #9
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I'm in agreement...its undeniable that factory engineers piss more knowledge than we'll ever accrue. Their products reflect such. I'm not a fan of airbox deletes, cuts, maulings. Injection systems, CV carbs, airbox and exhaust were designed to work together to attain best turn key, all around performance/response, fuel economy, emissions, the whole enchilada.
The 250 ran darn great right off the showroom floor, dinnit?

3 of my 4 (fuel injected) are dead stock...my older Ducati just minor, slight pilot system changes. All with original airboxes, no holes, chops, etc. All ageing reliably 25, 22, 13 and 2.... lotta years/miles, no issues, running superb, reliable.

Aside from diligent upkeep/maintenance...LITFA (leave it the F alone), my preference and personal motto.

However, i do respect the right of any owner to do what he/she pleases with their own property. If you are so inclined, have at it, chop, remove, mod your fuel/air delivery system to your desires.
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Old July 31st, 2020, 12:26 PM   #10
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Factory engineers also have different requirements than we do though. For example, emissions, which is something most people don't have to worry about here with a motorcycle. The newgen 250's exhaust is undeniably limiting power, and they are undeniably set rich from the factory. I'm sure the engineers had their reasons for doing so, but the end user can easily put a new exhaust on, tune the carbs, and get some not-insignificant extra HP out of it, while also improving the general operation of the engine. I see no downside, unless you have to pass emissions.
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Old July 31st, 2020, 01:38 PM   #11
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The short of all this, if you really want to get actual and meaningful performance GAINS out of your bike then you have to put the money into it. If you aren't willing to drop the money on a wideband O2 and dyno runs then the mods you do might not net a performance gain.

I just got my carbs back from ducatiman, I literally can't tell you how happy I am with the results. By far the best money I have ever spent on the bike.

Thankfully in my state I don't have to pass emissions and bought the bike with a full 2brothers (bike cost me $800), I can tune the piss out of the bike and it still be tagged.

If you want to go for a jet kit, by all means go ahead, you have the whole community here to help with questions and trouble shooting. Just know that without hard numbers we're all limited to how much we can help.
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Old July 31st, 2020, 03:33 PM   #12
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@Emu I didn't pick up on your username, now i gotcha ID'd.
The need for any tuning/jetting is first predicated on judging performance with truly clean, functioning carbs. Undeniable history....folks have justified misguided, experimental jetting changes, compensating for running issues due to carb setup. Hogging out pilot jets, (while other areas of the circuit remain clogged) a prime example. Extreme adjustments, way oversized mains, realities I've encountered.
If you are racing, trying to squeeze every bit out? Have at it.
As I'm not dicing with Valentino Rossi stoplight to stoplight on Main Street, USA, a serviced, maintained, unmolested factory setup more than suffices.
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Old July 31st, 2020, 05:46 PM   #13
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Quote:
Originally Posted by Ralgha View Post
Factory engineers also have different requirements than we do though. For example, emissions, which is something most people don't have to worry about here with a motorcycle. The newgen 250's exhaust is undeniably limiting power, and they are undeniably set rich from the factory. I'm sure the engineers had their reasons for doing so, but the end user can easily put a new exhaust on, tune the carbs, and get some not-insignificant extra HP out of it, while also improving the general operation of the engine. I see no downside, unless you have to pass emissions.
Some requirements for any major manufacturer is ease-of-use, reliability and durability. Not sure on exact terms, but I suppose 80-100k miles lifespan would be in ballpark. They'll tune engine on rich side intentionally in case owner runs across low-octane crappy petrol in boonies somewhere. Combined with hot day and that could spell disaster with knocking & pinging which will destroy head-gasket and puncture holes into pistons easily. So some extra fuel in 10-11:1 AFR range at WOT high-RPMs serves to cool down combustion, lowers NOx emissions and lowers peak-HP. Rich mixture also makes engine run smoother, something prospective buyers and owners would notice subconsciously.

For me, I only need engine & bike to last just ONE season and that's it. So I run high 13.0:1 compression with max-power 13.5:1 AFR on ragged edge of pinging/detonation and destruction. Bigger cams help high-end power and reduces dynamic compression to ward off knocking. Engine still requires 100-octane petrol (M+R/2) all the time. I think I may have detected some pinging at super-toasty 105F+ Thunderhill last year. I backed off ignition couple degrees just to be safe.
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Old August 2nd, 2020, 07:44 AM   #14
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