I actually own 2 1985 ATC250Rs, one of which I purchased brand new in August of 1984. Here it is:
Starting from the intake, the mods include:
Open air box (no lid, no front snorkel boot)
K&N Air Filter
38mm Mikuni Flatslide carb
Boyeson Dual Stage Reeds
3/8" Reed Cage Spacer
Trinity Stage III Porting
Weisco Piston
Answer Roost Boost Ignition Enhancer
Barnett Clutch
Bill's Exhaust Pipe & Silencer
Hi-Flite desert seat
Cooler Rack
Light & brake reservoir guards
GPS mount
I run 12/39 gearing with Skat Trak 22x11-8 8-paddle Haulers, and run almost exclusively in the sand dunes of Glamis California. This is my baby, and no one rides it except me.
My wife (48 yrs old) also rides a 1985 ATC250R (she also prefers the 3 wheeler over the quads). Hers is mostly stock, with the open airbox, K&N Filter, and Bill's pipe & silencer. She runs stock gearing and 21x12-8 Skat Trak Haulers. Here she is:
BTW, I also own a 2007 TRX400, mainly for the kids and other friends that we take to the dunes, as well as a 1985 Yamaha BW200 2-wheeler.
I grew up riding motorcycles in the deserts of SoCal, and spent a number of years racing in the desert back in the 70s & 80s. Glad to be a member of this site, and look forward to contibuting relevant knowledge, as well as gaining knowledge too.