I was wondering what jet to use in my carb after I build up my 400ex? Mods will be 416cc JE 11:1 piston, Hot Cams stage 1 cam, ported and polished head with stock valves, K&N filter and a White Bros E-series pipe. I'll be getting like 5 jets in the kit I ordered. I think the biggest is a 170. What would you guys try first?

 

first bolt your egt meter on and read the display, then there is no question about how to jet

 

Start out big then reduce until any bog goes away and do a plug check, but dont forget the needle and pilot jets either.

 

If it bogs at off idle, then it needs a pilot screw adjustment, right? Do you think I might have to step up to a bigger carb? I hope not, they're kinda expensive.

 

Spend the $450 for an FCR 39mm, it will make you regear. I can't believe what that carb did.

With the 416 modded as listed you will probably run a 165 main and maybe a 40 pilot.

 

a lot will have to depend on the weather your riding in, the elevation your at, running an airbox lid or not, etc. on average i would say around a 158 to a 162. now, these are keihin jets, not dynojets. i run a 45 pilot jet and my needle i change depending on temp. most of the time its on the 4th position.

 

The kit I ordered is a Dynojet kit. Are they no good? What's the difference between them and Keihin?

 

well i don't use dynojets. we have a keihin carb. dynojets have a different numbering pattern. make sure you know this. for example, a 150 keihin is NOT a 150 dynojet. the dynojets have a little different taper to them. this kit will come with a needle. you are suppose to use their needle if you use their mainjets. from what i hear, it is tougher to fine tune your bike with the dynojets because of the jets they make. for example, with the keihins you can get a 150, 152, 155, 158, 160, etc. with the dynojets, the numbers are more spaced out. many people use this kit so i am not saying its bad. personally, i would not use it because i can buy individual keihin jets for a cheaper price. but since you have it ordered already, its fine. also, disreguard my first post. the mainjet numbers i told you were for keihin jets. i am sure you will be somewhere in the ball park of these numbers. however, i have never used them so i can not tell you for sure. it will come with directions. i would just do a few plug chops and see what the plug looks like after some full throttle runs. jetting is trial and error. good luck