Just traded my 400 Scrambler for a 400EX. Decisions.... oh well! I live at 3500 feet elevation, and I'm not sure about the factory jetting on the 400ex. ALSO, gonna be doing some riding at around 8000 elevation. Do I need to make a jet change for this? Thanks in advance!

 

Check out your owners manual. It gives some advice for elevation jetting. Sorry that is all know.

 

The general rule of thumb is to rejet for each 1200' above sea level, so If you have stock jetting now you're likely running a bit rich at 3500' and would be way rich at 8000'. However, I've read on the forum that 400ex's come jetted lean from the dealer or factory (right or wrong?), so the best thing to do is pull the main jet & see what size it really is. Then you'll know whether or not you should rejet.If your ride is new & broken in, how does it perform at 3/4 to full throttle? If you don't get any misses or cutting out at full rpms,you probably are not lean.At 3500' I really would doubt that anyway.
Just to be sure about it, I would do a plug read. You'd possibly find that you are a little fat on the main with the electrode on the dark or black side, that is if you are running the stock jet. You could call your dealer or any good accessory shop to find out what the stock size is and after pulling the main you'll know where you are. In going to 8000' you'll surely have to drop at least one or two sizes on the main for the thin air. I'd go one size first & test ride & drop another if the plug shows rich..always better to err on the side of rich than lean.
Of course if you add anything to increase the air flow, then the above info will need to be adjusted accordingly.
BTW, I live at 3200' & in the hot weather I ride in the mountains at 7000'. I have to drop three sizes on my Warrior in order for it to run decently with the modifications on it.