Any 250ES is worth buying..buy it for sure!
As far as parts transfer is concerned most of the 86 will fit the 85.
The rear brake assembly is quite different as they improved the water intrusion issue in the earlier design. Also the carb has an improved cold start jet system as you meantioned.
I am sure that others will chime in with some of the other minor differences..
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)
The wiring is a bit different and I know the CDI units do not cross over (1985-one plug 1986-two plug). Snach up the parts machine and bolt the 1986 rear swingarm in your 85. The best 86 improvement is the in the rear diff and drive shaft design, the rest are "eh". I agree with the other guys...worth buying if you need a few things.
Disclaimer: "I have a problem"...I may not be the best person to give advice on this topic. This is how I justify the shelves and shelves of rusty old parts in my garage
Keepers:
07 BRP
86 big red "touring model"
85 big red "tortured model"
83 185s
05 rincon
04 rubicon
other interests : 250sx's, z50's, BW80's, LT80's...Oh Yea the kids too
the wheels are different they have lug nut style
and stickers, seat colors, helmet holder,
our original 85 we bought new, 2 - 86 police specials
250r dust runner
04 Yamaha kodiaK 450 snowbuster ! Brute Force 750 dust collector .
Bunch of es stuff I been buying for next builds....
Gone but lives on in my aching body the mighty 350x collection . A Beat 85 es im gonna rebuild