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Discussion Starter · #1 ·
I searched around and couldn't find any comparisons between the Sportisi and the Factory Pro jet kits. I am just looking for the best kit for my pre-gen 250. I have heard that Factory Pro>Dynojet but just give me some input of what you think.
 

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The tapers between needles are very tiny. The needle height will affect performance more than anything.


Stock Diameter/Taper

2.46 mm diameter
2.46 - 2.03 mm taper
2.09 - 1.19 mm taper
1.19 mm diameter

Factory Pro Diameter/Taper

2.44 mm diameter
2.44 - 1.83 mm taper
1.83 - 1.11 mm taper
1.11 mm diameter
1.11 mm taper


Dynojet Diameter/Taper

2.44mm diameter
2.44 - 1.92 mm taper
1.92 - 1.11 mm taper
1.11 mm diameter

(measurements made from the bottom surface of the top lip to the tip end)


New gen stock needles / Sportisi Needles

The Factory Pro and Dyno jet needle tapers are very similar to stock.
 

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So you would say the tapers are insignificant?
For normal street riding....yes. It's about how far the needle comes out of the jet. That's why shimming does so much. That fraction of a mm between tapers can be overcome by shimming. The needles mainly affect 1/4-3/4 throttle range anyway.

The main Jet is what you're concerned about if you're riding WOT and looking to get more power in the upper rpm range.

I doubt you'd be able to see it (taper difference) even on a dyno.
 

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Discussion Starter · #7 ·
Alright guess I'll just buy some mains after I get around to testing and work with the washers after some miles on the street. I already have put 1 on each needle on average how many do they put on a mostly stock bike? FYI I am running ethanol free so it will run slightly richer
 

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Alright guess I'll just buy some mains after I get around to testing and work with the washers after some miles on the street. I already have put 1 on each needle on average how many do they put on a mostly stock bike? FYI I am running ethanol free so it will run slightly richer
You need to move the needle height 1 mm or more, so 2 washers will get that. I too run ethanol free, but you're not running richer, the fuel (E-0) just has more BTUs (energy) than E-10.

Gasoline (conventional, summer) 114,500 BTU/gal
Ethanol (E10) 111,836 BTU/gal


Put in some Iridium plugs (CR9EIX) for a little better burn/combustion @ high rpms and use synthetic oil.
 

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Discussion Starter · #9 ·
I believe that ethanol makes you run leaner. For example you need bigger injectors when running alcohol than gasoline on the same engine. More fuel is needed for the same AF ratio with alcohol. I was just watching a video on koenigsegg and how they need to tune for different fuels around the world for the same AF ratio and performance.
 

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I believe that ethanol makes you run leaner. For example you need bigger injectors when running alcohol than gasoline on the same engine. More fuel is needed for the same AF ratio with alcohol. I was just watching a video on koenigsegg and how they need to tune for different fuels around the world for the same AF ratio and performance.
Tuning the AFR in a fuel injection vehicle is a little different than tuning it in carbs. Depending on your intake mods, one jet size can have you super rich or closer to being too lean.

Stoich(optimum burn) for E10 is 14.1, Stoich for E0 is 14.7- not a significant difference.

Your stock carbs are metered and jetted to give a stoich AFR as close to 14.7:1 as possible. Look at any Ninja 250 Dyno chart and thats what you'll see at some point in the rpm range.

Keep in mind 14.7:1 is the ratio to achieve a stoichiometric burn. However, this is not the target ratio for maximum power (just an optimal burn). 14:7:1 is great for cruising down the highway or coasting along down a small decline, when there is very little load on the motor. But under WOT, you have a huge load on the motor. WOT AFR of 12.8-13.2 is what you want on the dyno.

Temperature (and subsequently cylinder pressure) increases and can cause detonation. Adding more fuel (running rich) effectively lowers cylinder temperature creating a “cooler” and “longer” burn… this in turn creates more power per combustion stroke.

You can shim and it will enrichen this area (wherever stoich occurs on your bike) a small bit, but it will never be completely smoothed out in the stock engine set up. You will also find a slightly better throttle response and better cold starts.

Lucky for you somebody has already done the work for you. The Ninja 250 has been around over 30 years and a lot has been accomplished and some still improvements still coming on the new gens. Chasing HP can be a tiresome, frustrating, confusing and expensive task for some, for others it's a challenge. Many take the best results, without all the hard tedious work, implement them and roll on, happy with the results.
 

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Discussion Starter · #11 ·
In other words ethanol does make you run richer but only slightly :) It is times like these when I wish I had my own dynojet to test all my jetting out. Also I hear from different sources that the mains are lean or that they are rich? On a pregen what is the case?
 

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...In other words ethanol does make you run richer but only slightly :)
Technically....yes, but you burn more E10 than pure gas. For all technical purposes any AFR above 14.7:1 is lean any AFR below that is rich. So when people use the terms running lean or running rich it can be misleading.

....Also I hear from different sources that the mains are lean or that they are rich? On a pregen what is the case?
Both generation Ninjas have a point where the AFR is close to the technically lean side. It is not uncommon in the low range (2k-5k RPM) to hit the 15.0:1 mark under moderate to hard acceleration for a few brief seconds, but the engine is not in danger, providing the main jets are not too small. Because the Ninja 250 runs at high rpms, it needs to run rich in the 12.8-13.2 range. With bigger jets the AFR can get around 11.1

Here is something everyone jetting a bike should read. It's from an article on Pipe Jetting.
" Carbureted powersports vehicle manufacturers do not jet their carburetors perfectly, for two reasons. First, there are emissions considerations, mostly affecting the idle and midrange carburetor circuits. Consequently these circuits are jetted leaner than normal, and should be richened slightly for better performance. However, this rarely requires more than an adjustment to the idle mixture screw, and in some cases an adjusted slide needle height. Second, manufacturers ship their product to many different places across the globe. They purposely jet too rich on the main jet, the carburetor circuit that presents the most liability in terms of engine overheating. Therefore, all road-going powersports vehicles are jetted "fat" on the main jet. Contrary to what many people believe, but true nonetheless. Manufacturers do this because they cannot jet individually for each market, so they simply err on the rich side rather than the lean side, because the latter would present more problems. The fact is, engines are much more forgiving of a 3% rich condition than an equal lean condition, and just as importantly, few customers will notice a rich main jet, while nearly all will complain about a lean one."
 
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