400EX Jetting Help

[spcfraley]

I have an 04 400 EX that I am trying to jet. I has the factory exhaust with the baffle cut out and a K&N air filter. I started with a 158 but cut out badly on top end. I then went to a 155 and cut out in 3rd but not 4th or 5th. I then went to a 152 and still cutting out on high RPM in 3rd but does not cut out in 5th wound tight. I have preety much read anything I can find about jetting and can't figure why I would cut out in one gear but not the other. I have also tried with the lid on and with it off. Can anyone shed some light on my problem.

[SPE_Motorsports]

what was your jetting before you put the 158 in?

[400exrider707]

Usually they will clean out and run when they're lean, but will break up when rich.

Are you going to run with the lid on or off? What's the spark plug look like? What pilot jet are you running, where is the clip on the needle? Where's your fuel screw?

[spcfraley]

It ran a stock 148 before I made any changes. I also went to a 42 pilot jet but that should not change WOT. The needle is in what should be the 3rd notch since it has a non-adjustable needle in it and I didn't add any washers to it. As far as running with the lid on or off, it doesn't matter. Whatever gives me the best results. Let me know any more comments as I am open minded to anything.

[ridehonda400ex]

try a 150 main. i had an hmf on a old 400 and a 152 was rich. 150 worked best

[400exrider707]

Originally posted by spcfraley
It ran a stock 148 before I made any changes. I also went to a 42 pilot jet but that should not change WOT. The needle is in what should be the 3rd notch since it has a non-adjustable needle in it and I didn't add any washers to it. As far as running with the lid on or off, it doesn't matter. Whatever gives me the best results. Let me know any more comments as I am open minded to anything.

Since when do they not have adjustable needles? Again, what's the plug look like? Do some WOT runs, and hit the kill switch with it running wide open, come to a stop, yank plug, read.

Lid on or off is your choice for your conditions/preference, you just jet according to that. With the lid on, stock jetting will be fine. With the lid off, I'd drop the needle one clip, go to a 40 or 42 pilot (42 is quite popular and the choke never seems to be needed after this) and a 150 main. Then read the plug again and see what it's doing...