Really old kdx airbox mods!

On your year KDX, the air box cover is on the side of the airbox. On my old '84 (I bought it new and sold it in 1991), I drilled some 1" holes near the top edge of the airbox cover. I used a holesaw chucked up in an electric drill. I Can't say it really made much if any difference, so you might just keep it stock. If you do drill holes and plan on crossing some high streams, you should put some duct tape over the holes to keep water out of the airbox, then remove the tape in dry conditions.

If you make it easier for the bike to breathe, you will be getting more air for the same amount of gas. So, in theory, you should richen the jetting to keep the mixture the same as before. However, these bikes are generally jetted rich anyways, and you are only making a very minor change. You will probably be OK without changing your jetting.

IMO, the best thing you can do the performance of your '85 is improve the front forks by stiffening the springs and/or adding oil to improve bottoming resistance. Also, keep your brakes in good working order, as they were mediocre even by mid '80's standards, and a real weak point on the bike.

The '85 was a fine bike back in the day - I hope you have as much fun with yours as I did with my first KDX. :)

Don't know if I would do it - take a look at the area of the inlet on the airbox and compare it to the inlet (back side) of the carb. On my '88, I haven't measured, but I'd say the airbox inlet is larger in area than the carb inlet. Also, it's not really a torturous flow path from airbox inlet to air filter. So on my bike, I'm not going to unnecessarliy risk getting water in the engine (a distinct possibility in jolly old New England). Plus, Dave has first hand experience with this mod and he didn't think it made much difference. But hey it might make a cool sound. Just my O

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