My 400's filter has come off 2 times. The first time it turned side ways and killed the motor,(no air). The second time I looked just to make sure it was on OK when... nope its off again. The rubber lip is not very strong, I think maybe if you tighten it too tight it might pull it off or slide it off that lip. Or if you don't tighten it enough it will jar loose on a jump. My friends 400ex has never done it, but he doesn't jump as high as me. I jump some big jumps but they are usually doubles so the landing is not too bad. 10 or 12 feet high, and 20 feet long. I think the jumps that might be doing it are the 10' table tops. Those hit pretty hard when I land on flat ground. Has anybody else had this happen to them. Thanks.

 

I do alot of pretty big jumps on my 300ex and the filter always stays on. I just make sure it's slid up as far as possible and tighten down on it hard. I don't know what could be making it fall off. something just doesn't seem right. later

 

Yep, mine's come off, we have also had trouble with the clamp from the carb to airbox on the carb end coming loose. Make sure not to get any filter oil on the inside sealing surface of the filter itself, it acts as a lubricant and makes it easier for the filter to come off.

I have also broken the side and back mountings for my airbox from rough landings - big air is hard on things.....

 

Yes, my filter fell off the second ride. I told the dealer and he told honda, so that if I had problems with the engine later it would be covered. My buddy had the same problem on the same day. His started smoking bad, but honda stood behind it, and rebulit the 6 month old motor. I was shocked but thats what warranties are for. I tightened the dog doo out of mine, and haven't had any trouble for a year now. but guys I ride with have broken a few airboxes. I broke one with my front bumper, that was close racing.

 

was his smokeing the day it came off? Mine came off twice but I have not noticed any problems. When the dealer told you he would fix it later if you had any problems... how later are we talking about.. the warrenty later or years later?

 

I have ridden one time hard with the quick fix I gave my ex, and it didn't come off, and worked great. I pushed it on good - tightened it up good - and then took a very small drill bit and drilled a very small hole through the clamp and on down though the boot. I then took some rubber and made a gasket for a small screw, and screwed it down snug. The rubber is so it won't leak air, of course. I did it in the top, the bottom is sitting on the box. I didn't have any problems, and I don't think I'll have any in the future. It works and performs great.

 

I've broke the air box mounts (rear and side), my left arm, and loosened the air box hose from the carb several times casing big air jumps on my 400. Still haven't figured out how to fix the problem (other than jump better) as I still have a cast on my arm. At least it's summer and too hot to ride down here in Florida.

 

Does anybody know if the Hinson Air Box Rings, designed for the 250R, fit the 400EX? If they do it will solve your problem. The aluminum rings fit inside the airbox flange. You can really torque down the filter without caving in the airbox flange. I have them on my R and never had a problem with the filter falling off.

 

I dont know if you guys want to try this but it worked on my Grandpa"s
Spray a little hairspray on the rubber ring put the filter back on as fast as you can.
The hairspay will dry and then it will create a sort of weak glue that will hold the air filter on.
But it is not so strong that you can't take the filter off.
According to my grandpa this works great, and his filter has never come off.

 

I have had the exact same problems as Gabe, at least the bottom of the box is only $12 from Honda. For the filter, I am going to my local hardware store and looking for some aluminum tubing or PVC to keep the air filter attached, sort of like a pro design for Yamaha.