Do Jet-Kits & Air box Mods Work?

[FoxRacer400ex]

I just got a Yoshimura Slip-on exaust and a K&N airfilter with the outerwears. It seems to run good but I was wondering if I would get more power if I put in a jet-kit or maybe made some airbox modifications. Can anyone help me out?

fox, does your ex cut out on the top end??

[MadcapEX]

JET IT YOU WILL BE IMPRESSED,you havent even seen half of what the pipe and filter has done till you jet it.

[4punksdad]

ditch the paper filter.........open up the airbox & forget the jets.
I rejetted after opening the airbox & exhaust........only to find it was still running way too rich. I am about to install the stock jet again. I am currently running a 155 main.

I felt more power from opening the airbox than I did from opening the exhaust. I reinstalled the stock pipe to keep the cops off my back when trail riding.

[MadcapEX]

4 punks, what have you done to yours as far as mods,what was your stock mainjet? Mine came through with a 148,put the kn filter in and left the lid stock,went up to a 155 and the dynojet needle and the thing runs like a champ.

[FoxRacer400ex]

The quad runs perfectly in the top end and everything. Should I adjust the pilot jet or just get a jet-kit? I often have to ride through creeks and I dont want to flood if I have the holes in my airbox but if it is a big performance gain I will consider it.

fox look in ex tech and see how they did their airbox modification. this is what i'm going to do to mine. I've read a lot of these forums from people with this set up and they say that even after going thru water and mud that their airbox and filter still comes out cleaner than it did before they made the modification. supposedly the outerwears really work. i also heard that some people have noticed more power by opening the intake than opening the exhaust. I cant wait

[4punksdad]

here is one of my airbox lids........the other is a similar design, except it has 1" holes drilled in the top with fabric over them.

[rob-u/21]

I think that by taking off the airbox lid, putting a KnN air filter and using KnN's jet kit you gain from 2 to 4 horse power, I used to have on my ex and I did feel a big difference when I went from stock to that.

[VegasEx'r]

Have you caled Yoshi to ask how they recommend you jet? Usually, the pipe manufacturers have jetting recommendations to follow. If Yoshi does, it could save you some money by not having to buy a jet kit. I bought the dynojet kit, but now I don't think that the convenience of directions is worth the extra money (especially if you can get it for free). I have heard great things about the yoshi exhaust, have you been happy with it? Also, unless you are crossing streams that are so deep that they reach the top of your airbox, I think you'd be safe with the lid off (just go a little slower).

[Baley69]

can someone help me remember the guy in Florida that sells parts, believe his name is john, I think he supports or even operates these forums. I lost his #. Thx

Originally posted by Baley69
can someone help me remember the guy in Florida that sells parts, believe his name is john, I think he supports or even operates these forums. I lost his #. Thx

The link is at the top of the page,,,I'm guessing you mean Terry marcum????

[spincr4hire]

I ordered a Yoshi from Marcum's, along with a K&N filter and outerwear. I was going to order the K&N power kit, but Terry said it was a waste of money and that he would just send me the jets I needed, along with the other stuff....he recommended a 165 main for my area, and raising the needle one notch, along with running it without the airbox lid. My buddy did the exact same mod this weekend, but used the 170 main instead, it ran great as well. I'll let you know how the 165 does, hopefully after I do the install this weekend.

[FoxRacer400ex]

I could notice a nice HP gain when I put on the Yoshi but I baught the TEC Tunning spouts so I could keep the noise down around my house but let it roar at other places. I heard that you don't even get the power from the pipe until you jet it.