What are the differences between the '85 and '86 250r besides the seat logo?

I think the rear sprocket, or axle is different.
The front brake caliper.
The connector for the stator.
The CDI

That is all I can think of right now.

I know the axle bearing carrier is different as well as the axle ,I think the swingarm might be different to for the smaller Bearing Carrier,85 motor is black ,86 is Grey,And the springs in the front shock are a little different

86 ATC295R
86 TRX295R
87 LT500R
soon to come
86 ATC500R

The carbs are also different, the 85 uses a round type slide and the 86 uses a Keihin flat slide and the rear brake assembly and mounting is a bit different and as stated earlier the front forks use two spring instead of one in the 86 and the rear axle carrier is a better design in the 86. I have an 85 and love it but the 86's have some significant improvements

The bearings and swing arm joint are different as well.

Seat and cover are different too.
ERIC

Differences: Rear axel sprocket hub
Rear tires (stock)
Brake caliper linkage
Bearing carrier
rear shock resivoir mount
frame (footpeg mounts)
carburator
Seat/graphics
front light
handlebars (86 were lower profile)
front fork springs

There are some differences in the clutches, and some of the other internal parts.

Rear wheels in '86 were made by Enkei.

Internal valving and pressure changes for the rear shock as well.

I posted a big list of changes probably a year or so ago in this forum. With a little searching, you might be able to find them.