Jetting for higher altitude...

[atb400ex]

Hi everyone, quick question. I live in Peoria, AZ and the elevation here is about 1000 feet. This weekend im going up to the cinders in flagstaff, elevation about 7000. So first, do i need to rejet for the higher altitude? And if i do need to, do i need to go up or down in jet sizes?Thanks for everything.

[flyjum]

You will need a rejet or it will bog.
You need to drop down in size.

Say if you have a 140 main drop to a 132 or so.

6-8 points (rough figure is 1 point per 1000 feet at the same temp) Also the bigger the jet the bigger the diffrence.
For me on my quad I went from a 178- 172. This was from mesa az to young az(1000-5000).

Also you might want to raise you clip on your needle(if adjustable this will lean the whole range out for the less dense air).
The pilot should be ok but you could drop this one jet if you wanted.

Also temps makes a diffrence colder out more dense more fuel.
You still will need to drop jet sizes as it is a big jump in elavation.

Also you dont want to ride on the smaller jets in your home town.
Any mods on 400ex? have you had it rejetted?

[atb400ex]

Sweet man thanks! Yea i have a 416 kit, slip-on, air filter, and i think thats about it.

One more question, you said i should lower the clip on the needle if its adjustable. How can i tell if it adjustable and, if so, how do i lower the clip? Thanks

[flyjum]

Pull the top of the carb off and look at the needle. If its adjustable it will have 5 slots on the top with a very small c clip holding it on the throttle cable. You can raise or lower the clip to adjust mid throttle fuel.

Have you rejetted for the mods you have done?

Just copyed this from somewhere.

The Needle and Needle Jet
The needle and needle jet are the componets that primarily regulate fuel flow between 1/8 and 3/4 throttle. The needle jet is seldom changed in everyday tuning, but it's still worth mentioning the fact that it's there. The needle itself is a basically a tapered rod connected to the throttle slide. As the slide opens the needle is pulled upwards. The needle is tapered so that as it's pulled up, it takes up less space in the needle jet. This allows the fuel flow to be gradually increased as the throttle is opened. The needle has a clip that allows it to be lowered or raised in relation to the carb slide, which gives an overall richer or leaner setting. Raising the clip up a notch drops the needle down farther, causing a leaner mixture. Lowering the clip raises the needle up, causing a richer mixture. You can also get different diameters, and tapers of needles. If the clip is lowered all the way, and the mixture is still lean, you need the next size smaller needle. If the clip is raised all the way, and the mixture is still rich, you need the next size larger needle.

[atb400ex]

Ok I think i got it. Yea i rejetted for my mods but i never did anything with the needle, just the pilot and main jets. It seems to run perfect without having touched the needle.