Hot cam stage 2, Hmf Jetting.

[kcalexan83]

I have a Hot cam stage 2, HMF slip on and a Uni filter on my 400ex. I know absolutly nothing about jetting. I do know however that it needs jetted. lol. It has very little bottom end. It just wants to bog. Once you get in the midrange it runs decent though and on the top end it is ok. When I let off it back fires really bad. What would be a good starting point on the jetting? Thanks for any help in advance.

[LeGaCyGiAnT124]

I run a 155 main with the same setup, runs great.

[TheNewn]

It is obviously too LEAN if you have the stock jetting. Do NOT ride it anymore like this, it is bad for the motor without a doubt.

Backfiring is a sign of leanness, and you don't even really need the sign if you added those things to a stock bike without jetting.

Go up a couple few sizes on the main jet, up one on the pilot, and raise the needle maybe. It all depends on where you are. A 155 main at least is a good starting point.

Do you have any air box mods at all? lid off? Filter?

[kcalexan83]

The only thing done to my atv motorwise are Uni filter, HMF slip on and the stage 2 cam. Will there be any difference between the jetting on mine and Legacy considering he has a 416 kit?

[kcalexan83]

I stopped at the local shop today and the guy told me to put a 152 main in it and turn the screw out 3-1/2 turns. He said he jetted a 400 with the same mods that way and it ran perfect. I put the 152 in it and wasn't sure which screw he was talking about so I put it back together and it won't even start now. He was closed by the time I got home so I couldn't call him. I know I sound like an idiot but I truely don't know anything about carbs.

[TheNewn]

I'm sure he was talking about the fuel mixture screw on the side of the carb.

GET A SERVICE MANUAL.
Look online for a blow up diagram of 400EX carb, it will show every part very simply laid out and how it goes together.