adjusting 400ex air screw

[Boone]

Hi all,
I just bought a used 400ex and it runs great except for it blubbers a little from just off idle to about 1/4 throttle. I'm assuming the air screw needs to be adjusted. Here's my problem-
how the do i get at it without taking the carb off? Is there a special tool? I'd like to do it while it's running, but theres no way to get your fingers in there without burning the **** out of yourself. thanks in advance for any tips.
Boone

[400exdad]

Its a real pain. You have to do it with just the right size screw driver at about a 45 degree angle. In other words, you turn it about a 1/8 of a turn at a time with the corner of the screwdriver blade.... make sense? Your riding gloves may help or try to do it before it gets good and hot. Inward is leaner and out is of course richer. If someone jetted for a pipe and took it off, I would play with the airbox lid. Take it off and see if it helps. One more thing. If its starts easy when its cold, (not started for the day), I'd bet its had the pilot changed. With the stock pilot, its very cold natured and a little hard to start.. Good Luck:D

[mikeboone]

It is actually a fuel screw. The carb does not have an air screw. If you turn the screw clockwise; it will make it leaner. Turn counter-clockwise to make it richer. By turning it in you are reducing the fuel flow. It def. is too lean--ANY pipe will compound the already lean condition from factory. It is jetted lean to control emmissions.

[Boone]

I took the carb off just to see what changes were made.
Here's what I have, White bro's E series slip on, #155 keihin main jet, #42 keihin pilot jet, stock needle jet (3rd groove down), pilot screw 3 turns out, (3) 1-1/2" holes in air-box, K&N filter with pre-filter. I live in Wisconsin and I'm not sure what eevation we're at.
Does this sound like a good set-up to you guys? or would a K&N or dynojet jetting kit be better.
I ran out of time before I got a chance to mess with the pilot screw. Thanks again
Boone

[Boone]

Thanks for the help,
I ended up at 1-1/2 turns out and the blubber is gone.


Boone

[zuLi0]

Originally posted by 400exdad
Its a real pain. You have to do it with just the right size screw driver at about a 45 degree angle. In other words, you turn it about a 1/8 of a turn at a time with the corner of the screwdriver blade.... make sense? Your riding gloves may help or try to do it before it gets good and hot. Inward is leaner and out is of course richer. If someone jetted for a pipe and took it off, I would play with the airbox lid. Take it off and see if it helps. One more thing. If its starts easy when its cold, (not started for the day), I'd bet its had the pilot changed. With the stock pilot, its very cold natured and a little hard to start.. Good Luck:D

So because its hard to start, on what part of the pilot jet will help that? And changing the pilot jet, what else will that effect besides starting it?

-charLie
eXriders deveLopmenT TeaM

[400exdad]

Sorry for the late reply zulio. I've been under the weather the last couple of days. Changing the pilot jet, with just stock motor, will help it start better when cold. I've done it to both my 300 and 400. They are just to dang lean from the factory! I'm not sure if they do that for emissions or what. Anyway, my 300 was very cold natured before I made the change. The down side to going up on the pilot can be a condition of being too rich at idle and just above idle. This would result in the quad being sluggish until 1/2 throttle or so was reached. You could also see some black soot on your plastic depending on which pipe you run. Alot of folks here have removed the choke completely and bumped up the pilot jet to compensate for cold start. I think they pump the heck out of the throttle to nurse it to life when cold. I am not racing and don't really need every pony the 400 is capable of so I'm leaving the choke in for now. Hope that helps.

[96300ex]

what pilot did you use on the 300?

[BornOnFire]

I have found that you can use one of those screw driver bits that fit into a drill to adjust the fuel screw with ease. I am running a 142 pilot and a 152 main with 12- 1" holes in the lid, E-Series Slip-on and I seem to be pretty good. I do have problems cold starting the motor but, if I pump the throttle 7-8 times, it will fire right up.

[brian400ex]

Wow a 142 pilot jet!! Who needs a main jet when you have a 142 pilot jet. I bet you meant to say 42. Just being a pain in the ***. LOL!

[BornOnFire]

Yeah! I have a Holley Four Barrel on my quad! j/k Yeah, I meant 42 pilot thanks for the correction!!!!

[400exdad]

In my 300, I think I'm running the 38 pilot that came out of the 400, but I better look at the jets I've got lying around and confirm that. I'll post back and let you know for sure.

[400exdad]

Sorry, I don't know which pilot jet I'm running in the 300.... probably the next step or two up from stock.... It is definately not a 38.... I've got three of them in my jet box! :)