Dynojet / Tuning questions

Shenal · July 15th, 2020, 01:45 PM

hey all, 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 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!

DannoXYZ · July 15th, 2020, 03:52 PM

Hi Shenal and welcome to Ninjette!

Be aware that jet-kits are for tuning after making flow-increasing upgrades. This should be done on dyno with printed out AFR curve. Then you make an adjustment with jet-kit to get AFR into most-powerful 13.5:1 AFR range.

Now, most people throw jet-kits on without making any flow-increasing changes. Slip-ons and air-filters do not increase flow. This has been tested numerous times on dyno. Only full-exhaust upgrades increases flow on exhaust side. On intake, you'll want to install larger intake-valves and port head (or install 300 head). Stock airbox and filter flow plenty enough for 250cc engine as they are same size as airbox & filter on a CBR600RR; bike with 5x power and 5x airflow.

What you see in terms of reported jetting changes are due to clogged and dirty carbs. People let or get a bike that's been sitting around for months, years and end up with clogged carbs. They try to do cursory cleaning with spray-cleaners that doesn't do anything. Finally in frustration, they install new & larger jets. It's not the larger size that fixed their problem, but new unclogged jets that fixed it.

But there's other areas of carbs that wasn't cleaned or fixed such as fuel-circuits and pilot-screws and O-rings and float-valves and float-heights. So over time, bike starts to run badly again, so it must be replacement larger jets are still not big enough, so they go bigger yet to make up for clogged fuel-passages. It's an endless progression that never actually addresses problem: dirty & clogged carbs that needs full refurb and restoration.

Bottom line is unless you make dramatic changes to engine such as big-bore pistons, head porting & polishing along with full-exhausts, air-flow will be similar to stock and optimum jetting will be around stock anyway. My race bike has full-exhaust, K&N filter, higher-compression pistons, minor porting of intake-passages. And it was tuned on dyno by sponsor of our race-series Spears Enterprises. By looking at dyno-charts, he actually downsized my main-jets by 2-sizes to get more optimal AFR. That's with 25% more flow than stock and 30% more power than stock and it still needed smaller-than-stock jets. We could've gone to 3-sizes smaller for even more power, but wanted to sacrifice some peak-power for safety-margin in case we got bad gas or had extra hot day at track.

Here's dyno of bone-stock Ninja 250. Note how rich AFR is under WOT above mid-range. Target AFR for max-power is dashed-line 13.5:1 ratio. Its easily 30-35% way, way too much fuel.

So... these bikes are pretty well optimized from factory. You're not going to out-do their engineers. Best to leave engine alone and spend money and time doing suspension-upgrades. You'll have more fun with bike and get better bang-for-your-buck and time doing that than trying to extract any more from engine.

DannoXYZ · July 16th, 2020, 04:04 PM

Here's another example of dyno-tuning. This time with European 250 which is fuel-injected. This allows for much, much easier, faster and more precise adjustments at dyno-shop. You just adjust 3D maps on factory ECU in 30-seconds with couple clicks of mouse instead of spending half an hour pulling carbs, swapping jets, needles, needle shims, adjusting pilot screws and putting carbs back in. Imagine doing that 10x in a row in single day! On certain turbo cars, I've done as many as 30 dyno-runs in day to dial them in at multiple boost levels.

You also have much more precision with smaller adjustments with EFI. Factory ECU maps aren't bad but still too rich from factory. Besides leaning out mixtures for more power, you can also optimise mixture flat across entire RPM-range for maximum-power at 13.5:1 AFR. With zero physical mods at all, it's possible to get +15% increase in power from just fine-tuning ECU maps alone!

July 15th, 2020, 01:45 PM	#1
Shenal ninjette.org newbie Name: Shenal Location: North York Join Date: Jul 2020 Motorcycle(s): Ninja 250 Posts: 2	Dynojet / Tuning questions hey all, 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 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!

July 15th, 2020, 03:52 PM	#2
DannoXYZ ninjette.org certified postwhore Name: AKA JacRyann Location: Mesa, AZ Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot. MOTY - 2018, MOTM - Nov '17	Hi Shenal and welcome to Ninjette! Be aware that jet-kits are for tuning after making flow-increasing upgrades. This should be done on dyno with printed out AFR curve. Then you make an adjustment with jet-kit to get AFR into most-powerful 13.5:1 AFR range. Now, most people throw jet-kits on without making any flow-increasing changes. Slip-ons and air-filters do not increase flow. This has been tested numerous times on dyno. Only full-exhaust upgrades increases flow on exhaust side. On intake, you'll want to install larger intake-valves and port head (or install 300 head). Stock airbox and filter flow plenty enough for 250cc engine as they are same size as airbox & filter on a CBR600RR; bike with 5x power and 5x airflow. What you see in terms of reported jetting changes are due to clogged and dirty carbs. People let or get a bike that's been sitting around for months, years and end up with clogged carbs. They try to do cursory cleaning with spray-cleaners that doesn't do anything. Finally in frustration, they install new & larger jets. It's not the larger size that fixed their problem, but new unclogged jets that fixed it. But there's other areas of carbs that wasn't cleaned or fixed such as fuel-circuits and pilot-screws and O-rings and float-valves and float-heights. So over time, bike starts to run badly again, so it must be replacement larger jets are still not big enough, so they go bigger yet to make up for clogged fuel-passages. It's an endless progression that never actually addresses problem: dirty & clogged carbs that needs full refurb and restoration. Bottom line is unless you make dramatic changes to engine such as big-bore pistons, head porting & polishing along with full-exhausts, air-flow will be similar to stock and optimum jetting will be around stock anyway. My race bike has full-exhaust, K&N filter, higher-compression pistons, minor porting of intake-passages. And it was tuned on dyno by sponsor of our race-series Spears Enterprises. By looking at dyno-charts, he actually downsized my main-jets by 2-sizes to get more optimal AFR. That's with 25% more flow than stock and 30% more power than stock and it still needed smaller-than-stock jets. We could've gone to 3-sizes smaller for even more power, but wanted to sacrifice some peak-power for safety-margin in case we got bad gas or had extra hot day at track. Here's dyno of bone-stock Ninja 250. Note how rich AFR is under WOT above mid-range. Target AFR for max-power is dashed-line 13.5:1 ratio. Its easily 30-35% way, way too much fuel. So... these bikes are pretty well optimized from factory. You're not going to out-do their engineers. Best to leave engine alone and spend money and time doing suspension-upgrades. You'll have more fun with bike and get better bang-for-your-buck and time doing that than trying to extract any more from engine. Last futzed with by DannoXYZ; July 15th, 2020 at 10:25 PM.
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July 16th, 2020, 04:04 PM	#3
DannoXYZ ninjette.org certified postwhore Name: AKA JacRyann Location: Mesa, AZ Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot. MOTY - 2018, MOTM - Nov '17	Here's another example of dyno-tuning. This time with European 250 which is fuel-injected. This allows for much, much easier, faster and more precise adjustments at dyno-shop. You just adjust 3D maps on factory ECU in 30-seconds with couple clicks of mouse instead of spending half an hour pulling carbs, swapping jets, needles, needle shims, adjusting pilot screws and putting carbs back in. Imagine doing that 10x in a row in single day! On certain turbo cars, I've done as many as 30 dyno-runs in day to dial them in at multiple boost levels. You also have much more precision with smaller adjustments with EFI. Factory ECU maps aren't bad but still too rich from factory. Besides leaning out mixtures for more power, you can also optimise mixture flat across entire RPM-range for maximum-power at 13.5:1 AFR. With zero physical mods at all, it's possible to get +15% increase in power from just fine-tuning ECU maps alone!