I think i know the answer to this question but i want to be sure. will and 87 gas tank fit into an 85 with no problems? I am pretty sure that it will but i want to make sure.

I am not sure either, but the man I recently bought my 86 from has an 85 gas tank and said it should fit. All parts on all 84 - 87 should be interchangeable.

The 87-88 Fuel tanks are different than 84-86 tanks. Yes it will fit but it is not a direct fit. IIRC you will want to use the tank straps that match the tank and you will have a little interference inside the tunnel which will prevent the larger tank from going all the way up into the tunnel which will require some trimming or work with a hammer.

You should also install the expansion tank from the 87 as well. It is located above and infront of the right rear wheel.