I want to take off my air box lid to get more power what size jet do i need to get? Also if i take out my spark arrestor do i need to rejet again? I mainly go to glamis but this weekend i am doing a day trip to dumont. Any changes then with the jets?

Can't help you with your specific question but these guys can, there is also jetting sticky in there somewhere.

www.Z400central.com

I put a pro circuit pipe on mine and didn't have to rejet anything. I ride up near Dumont and haven't had any problems.

http://www.albaaction.com/service/jetting.htm#LT-Z400

these recomendations are pretty damm close. ive used em all and they work!

Ditto on the ALBA specs.

If you aren't interested in the complete ALBA kit, you can get the air filter and jet kit. They have a new needle (stock shim pack, retaing clip on the thrid notch from the top), a 160 main jet, and keep the stock pilot jet.

Make sure that if you are going to re-jet your Z400 that you buy 4 new carb fuel bowl screws. I guarantee that you will strip them out. I have had 2 brand new Zs that I re-jetted and stripped them both out (bought 4 new screws when I rejetted the second).