I just got a 1999 400EX a few days ago and I have a few questions for you guys.
1. Can you speed shift a 400EX. I know I can but I Don't know if I am suppose to. The 4 stoke sounds a little weird to me when I shift without letting off the gas.
2. How do you tighten the chain.

3. I was told to run the tires at 4 psi this seems a little low to me what do you think.

 

To tighten the chain, loosen the socket head capscrews on the rear of the swingarm, then insert a spanner nut wrench (or screwdriver) in the slots on the left side of the bearing carrier and pull towards you, that spins the bearing carrier and moves the axle to the rear, thus tightening the chain. I believe the correct tension is 1 and 3/8" slack. Keep in mind the chain will get tighter as the suspension compresses. Don't oertighten it.

I have seen it posted, not sure by who, to run around nine to ten pounds of tire pressure if you are going to be jumping the quad, to prevent bending the rims. I run 5 lbs. and haven't had any problems. I don't do a lot of jumping either.

Good or bad, I'll not be shifting with out at the least letting off of the gas. It would takes a lot to convince me that it is ok to shift under power with out letting off the gas or using the clutch.

Good luck.

 

I run about 9 psi in the rears and about 7 psi in the fronts if I am out jumping. This will help keep from smashing the wheels, but will provide a very rough ride and will tend to make it loose in the corners.

4 psi worked well for me in some of the aftermarket tires, but the stock tires sidewalls are pretty weak, and will fold over in the corners pretty badly at that pressure, try different settings and see what you like.... 6 or 7 in the rears with about 5 in the front is probably a good compromise for general hard riding without big jumps.

As for the chain adjustment, check this link on GT Thunder. They have an interesting way to set the chain.

As for speed shifting, it can be done, you may have to back off the throttle just a little in some gears. For me, the fastest way to shift when I'm really getting it, is to "slap" the clutch. This is really abusive to the clutch, but that's why they make replacement discs. Basically never let out of the gas and give the clutch a little slap between gears (disengage it about half way with a quick slapping motion), this disengages the clutch ever so slightly to allow for quick, easy, fast shifts when under heavy power. Be prepared for the front to climb violently in the lower gears.. Rule of thumb, I don't use the clutch for shifting when riding moderately (just back off the throttle and click the next gear), I do use it when riding all out or drag racing...

 

I would say use the clutch, especially if you are the type that doesn't like taking apart bottom ends on a regular basis.

 

Thanks for the advice. As far as the speed shifting goes I always use the clutch but I sometime I don't let off the gas. I just won't to know if that is a bad thing to do.

 

Just hard on the clutch..... Easy & not too expensive to fix though....