The 250sx with the white tanks and headlights are the 86 and 87 models. There were not as many made as there was in 85, which are the ones with the red tank and headlight.
Honda made several improvements to the 86/87, the biggers being a competly differen swingarm and rear end. The carb is different too.
If you find a good deal on a 86/87 jump on it, I have three and they are great trikes.
ATCnut
82 185s - sold
83 200x (hopped up)
84 200x (stock)
84 70 (lost this one to the DMV)
85 70 (soon to have lights, a foot brake, and CDI ignition)
84 200es (parts trike) - sold
85 350X (the best)
85 350X (siezed motor, dream of a poweroll kit someday)
85 250sx (frame was trash, got parted out)
86 250sx (the tractor)
86 250sx (a nicer tractor)
86 250sx (an even nicer tractor)
87 200x (parts trike, its really rough, a dog was chewing on it for a while)
87 250es Big Red (the tank!!)