New to me 89 kdx and lots of questions

[Green Bastard]

Just picked up a pretty decent 89 . The motor was just done but the rest of the bike is showing its age.
I bought the bike for cheap with intentions of just using it as a trail beater to ride with my son on his little 80 .
Now after some seat time, it has reminded me how much I miss dirt bikes ... Not to mention these KDX'S are just so damn fun and easy to ride.
So after some reading on these forums and looking at some of the rebuilds you guys have done on some of the older ones, I am thinking Id like to breathe some life back into this old beauty.
I will have lots of questions... but for starters .. Ive read a bit about swapping kx forks onto these bikes ? Can someone tell me an exact model and what years are best and if its a direct swap ? Is this a better and easier way to beef up the front end ? Or am I better off just rebuilding my stock forks ?
I am probably a little big for the bike to begin with at 6 ft tall and 225 pounds and the suspension is pretty bagged out , so I would like to tackle that first.
Oh And another question . I pulled the seat off to check the air filter and was shocked to see the air filter right there in the air box with no lid or any type of cover other than the seat . Is that normal ? or is my bike missing an airbox lid ? It doesn't look like there is room for any type of cover so maybe that's just the way they are . Just looked odd to me. Ive had a few Hondas in the past and the airboxes were always closed in.
Thanks

[6 Riders]

Forks; The 89 forks are pretty week, so a swap would be ideal. KX 500 forks and klx 300 forks are a direct swap as far as the triple trees go. Might need a wheel with the kx forks and you will need the brakes. With some machining work, the KX 125/250 front ends will swap, you will need the whole front end trees to wheel for this swap. You can also go cheap and use an H series front end, the handling will be 100% better with these forks compared to the 89 forks. Again you will need the brakes. I would also give the suspension bearings some love, just replace them, they are (most likely) really old.

The airbox is missing the lid, but it is a common mod to remove the cover and re-jet the bike.

[Green Bastard]

Thanks for the reply . Sounds like the fork swap shouldn't be too difficult . I will have to do some more reading and decide what way I want to go .
I also need new bars, so the type of trees I end up with may be a factor in that as well.
As for the air box lid .. I kinda figured they wouldn't leave the air filter that exposed from the factory ... now to find a lid . I looked on ebay already. Lots of airboxes, but none with lids.. go figure . I have been known to try to cross creeks that are deeper than they look ... So I should probably run the lid . LOL
Anyone know if the 95+ KDX's use the same airbox ? They look the same . That might make finding one easier.

[bufftester]

The fork swap is not as difficult as it sounds, and worth the improvement in handling. The most important point for any suspension work is to properly spring the bike for your riding weight regardless of what forks/shocks you have on. The lid is not really needed, the bike performs better without it. Even with the lid if you submerge the bike it's sucking water. If you do put the lid back on you will want to run through the jetting guide to dial the bike in as it will change the way it runs. As far as size, I'm 6' and 235 and never had an issue once I properly sprung it. A set of bar risers or a higher bend bar will give you more cockpit room.
Oh, and congrats on the purchase!

[Green Bastard]

Thanks bufftester. I will look a little deeper into the fork swap . I may just do the forkseals and leave it stock . .. or maybe just add stiffer springs. I like this old bike and want to freshin it up for sure . I just haven't decided how much money and time I want to put into a 25 year old bike. I am just gonna do the basics and get it trail worthy ... sprockets and chain..bearings and tires etc and ride it a bit . I may look for a newer 2000+ kdx 220 in the spring for myself and hand this one down to my son.. or maybe the wife can ride it if I shave the seat a little .

[Dekon]

Go for the proper springs for your weight/riding ability. Made a huge difference on my '89. Feels way more balanced.