Losing power, top speed is ~70 at 9,000rpm, WHAT'S GOING ON???

[alex.s]

the correct solution is to put in the correct jets for the air flow your setup creates.

[alex.s]

Originally Posted by ninjamunky85

You've replaced your air filter with one that flows more air, and added an aftermarket exhaust, which also flows more air. So you've got all this extra air going through the motor, but no more fuel, meaning your running lean. These bikes are already jetted on the lean side from the factory to make the EPA happy.

Anyway you need to re jet your carbs, or just put the stock air filter and exhaust back on. Good luck

@JLinde1339 - here is the solution that was already offered.

[JLinde1339]

So, to anyone running a K&N R-0990, with stock exhaust, what size jets are you using?

[Kevin2109]

Originally Posted by JLinde1339

So, to anyone running a K&N R-0990, with stock exhaust, what size jets are you using?

dynojet 100 works pretty well

[alex.s]

"the right jet" depends entirely on your current situation with the bike. it changes. if you want optimal jetting then you need to figure it out for yourself. thats why jet kits come with multiple jets. because its not always the same.

[JLinde1339]

Originally Posted by Kevin2109

dynojet 100 works pretty well

According to the ninja 250 wiki, thats a size smaller than stock, Unless dynojet has changed their sizing, correct?

[Kevin2109]

Originally Posted by alex.s

"the right jet" depends entirely on your current situation with the bike. it changes. if you want optimal jetting then you need to figure it out for yourself. thats why jet kits come with multiple jets. because its not always the same.

This

Originally Posted by JLinde1339

According to the ninja 250 wiki, thats a size smaller than stock, Unless dynojet has changed their sizing, correct?

idk about the pre gen but stock on is 96 or 98, cant remember off the top of my head

[JLinde1339]

I guess my point here is trying to find answers to these questions are not easy, as I'm sure anyone who had done this knows. But every thread about carbs is like groundhog day around here. Its always try cleaning the carbs, seafoam, rejet. Even the ninja wiki offers info on how to do it, but only goes on to 112 main jets for K&Ns or pods for the article on rejetting. And I don't know about the OP, but shelling out $100+ on a jet kit is not always a viable option. Just a ballpark answer would do, like you may need to go up to 122 mains. After buying two sets of jets, and not getting any tangible results, I decided that, since I can't wait another week to get the next size up, why don't I tackle the problem in reverse, so instead of increasing the fuel, decrease the air. That gave results, and ones that seemed worth sharing, since we both had nearly identical symptoms and failed solutions.

[alex.s]

don't get me wrong. its a good troubleshooting tool. but that's all it is. these engines have a very small range for jetting. jetsrus.com, buy the cheap jets for what you need based on where you need to go from your current jets. you can do plug checks and other troubleshooting methods like choking it (you are choking it by restricting the airflow) or even using the fuel enricher circuit ('the choke') to see how it effects the mix. but like i said, those are just tools for troubleshooting. you need to have correct pilot and main jets with the correct needle transition.

when people have the problem of incorrect fuel mix, they blame this and that but the fact is carbs are simple, they work very simply, and when they are setup wrong they dont work. they are responsible for the fuel mix, so if everything is how it should be (in other words nothing is falling off and you are using the components you want to use, ie- air filter, exhaust, etc) and the mix is off, then guess what, your jets are wrong.

[choneofakind]

Originally Posted by JLinde1339

So, to anyone running a K&N R-0990, with stock exhaust, what size jets are you using?

stock main jet on a pregen is 105.

I had my intake lid cut open, and a full system running well (a little rich at the top end, but it pulled hard so I was happy) with 108's and 3 washers on the needles.

with a stock exhaust and pod filter, I would try 108's and 110's, likely with 2 or 3 washers on the needles. That shouldn't take long too get jetted, especially without the airbox.