installed new cam, what jet do i use

[05 ex rider]

i have an 05 400 with a k&n, slip-on yoshi pipe, moose raceing cdi, and i just put in a stage 2 hot cam. i was just wondering what my jet size should be. it was jetted when i got it. with a 142 main and 38 poilt. also i am going to re-move the choke. i had a friend install the cam he went to uti and thats what he does for a living. but he frist told me it needed a 155 main then after it he was done he said it was fine with the 142. i dont know if he just didnt want to mess with rejeting it or what.

[400 SS EX]

After I installed my stage 2 cam I did not rejet and it runs fine runs it seems like your running a bit lean as it is. I think the is actually the stock setting! Try about a 155main, 40 or 42 pilot ( i have 40 but think I need a 42) And put the needle clip on the 3rd or 4th position.

[05 ex rider]

ok thanks i will try that this weekend

[GPracer2500]

Stock main is a Keihin 148. The 142 that's in there is most likely a Dynojet jet which uses a different scale. If you start changing your jetting, make sure you only make one change at a time.

Might want to consider a high compression piston with a stage 2 cam.

[stang233]

Can i run a stage 2 cam and see any gains until i get a high comp piston. Or even with a high comp piston can i still run the stage two. I am thinking i might not go with a piston so i should just go stage 1

[400 SS EX]

Originally posted by stang233
Can i run a stage 2 cam and see any gains until i get a high comp piston. Or even with a high comp piston can i still run the stage two. I am thinking i might not go with a piston so i should just go stage 1

Yes you will see a power gain WITH a stage 2 and WITHOUT a piston but if everything is already apart and you can get a piston for about a 100 bucks why not?? But if I where you and was running a stock piston I would get a stage 1. Stage 1 is more of an all around cam stage 2 is great for MX, TT, and flat track racing , but terrible in trail situations.

[GPracer2500]

Here's the deal with cams and compression. We ususally talk about compression in terms of 10:1, 11:1 etc. That is a static compression ratio. The measurement that ACTUALLY matters is dynamic compression. This measurement of compression takes into account the fact that the intake valves are still open when the piston begins the compression stroke. That's the primary way dynamic compression is linked to cam specifications. The actual compression a piston generates doesn't begin until the intake valves close.

That's why aggressive cams with lots of intake valve lift/duration may require a high compression piston. You need some of that extra compression to make up for the what was lost out of intake valves.

I've seen first hand the results from running a cam intended for a high compression engine in a stock engine--power loss everywhere over stock (it was a CBR900RR, dyno tested).

I wouldn't say a 400EX with a Hotcams stage 2 and stock compression would loose power over stock because I haven't seen that settup dynoed. But a stage 1 cam would be more "appropriate" for a stock compression engine.