Most should interchange between the two, with the exception of the rear axle--it will work but Honda made the sealing(to keep water out) better on the 86-87 SX's. Carbs are slightly diff also I think(cold start). But I believe the majority will, you can always check the online microfische to be 100% sure.
Did you see it on craigslist?? If so for the 75 it's not a bad deal.
Good luck on the deal.
Racerxxx
1985 Honda 125M (My first Trike--Still have it)
1986 Honda 250SX
1981 Honda 110
1982 Honda 110
1986 Yamaha YFM80 (Sons quad)
Past rides: 1983, 1984 200X, 3--1985 Kawasaki T-3
1987 CR-80, 70's vintage XR75, RM 370
There's very few differences, not really anything to worry about. $75 is a bargain; you will get that much in parts out of it.
You can run the '85 axle in the '86 if you swap the swingarms. The '85 axle is a downgrade though; but if you ever kill your rear end gears you have an option.
I bought another '85 SX for parts about three years ago. Cost me $50 and it looked like a 'parts' machine. Within a few hours of having it home, I had the engine running strong and found out most everything (except kickstart and brakes) worked well. I plan on building this trike up when I get back this coming winter.
BUY IT!
15T3FN1 CE/FI/SI with a Class A; Some of you might know what that means.
1986 ATC 200x, Gathering parts for a 200sx build.
1985 ATC 250SX 25" tires, extended swingarm, snorkel and other mods for Alaska adventures.
1985 ATC 250SX, Big plans for this one...
1985 ATC 250ES, Big Red
1984 ATC 125M's, 1.5 of 'em
1983 ATC 110, BLUE!
1974 ATC 70 Pink?