1986 yz250 info

[bronkorob]

so im looking for parts for an 86 YZ250. it needs a top end, but i found an 85 that runs that would be cheaper than a top end, and it would be nice to have a few spare parts, and i can rebuild a complete motor on the side. anyways, will an 85 motor work in an 86 frame? the cases have the same part number, but where there any drastic differences between the years. what is the year range for this generation motor and frame?

[bronkorob]

also what year motors will fit in the frame besides the 86?

[Dwight_Rudder]

The 85 pipe is better for sure. I think the engines are similar.

[buzzard111]

i used to have an engine that was made up of 83 and 84 parts in my 86 yz 250, pictures please

[bronkorob]

i will put pics up soon. ive got some leads on 85, and an 89 running motors for dirt cheap. now i have to figure out which ones fit. right now the bike is in a few pieces so i could check the cylinder. i can post some pics soon. this week im taking the cylinder to a shop to see if i can salvage the cylinder. if its more than just bore and new piston and the other year motors i found dont fit, i may just part it out.

[Robmx29]

Look into having it resleaved, if you are restoring or even if it is just for a weekend ride bike it might be worth it to keep it original.

[bronkorob]

ok let say i do get this bike running again. i know this generation YZ is not the most popular out there. are there any 80s YZ gurus out there, any good websites for these bike? it looks these bikes arent the most popular even restored, so im not concerned too much about factory original parts. was this a good year for the YZ? the carb needs a new float, and idle screw. im having a problem finding just the float for it. i seem to only find the plastic independent type. any ideas?

[bronkorob]

oh yeah here is a pic of the bike as of today. going to take the cylinder in today to get checked out. unsure of the bore hopefully it can be honed or bored again. the piston was no help, no recognizable part numbers on it and no +0.xxx numbers stamped on it. maybe its stock? i guess this is the point where i determine if its worth rebuilding.

[bronkorob]

i got a good cylinder! so the rebuild is on. just took the motor out and did a good cleaning on the frame and ordered some parts. there is some light rust on the typical spots where the boots rub, but otherwise pretty nice everywhere else and no dents or serious bashing on the bottom. I had some IMS pro series pegs i had for a bike i sold laying around. did a little grinding on them and got those to fit too! im kind of amazed at how small the original pegs were compared to modern bikes. anyways here are some pics for you guys.

[Robmx29]

That bike looks nice, you have a great start to the project. I am kind of partial to these years of bikes, 86-89. They probably aren't worth too much when done, right now any way, but maybe some day. They look cool though.

[Robmx29]

check this out. www.kx125project.blogspot.com its my current project.

[BruceD_500]

83-86 engines should be very similar 87 is a bit of an oddball I think.

Then 88-94 are similar .

You'll find the engines I've described to be similar but over the years little things will change . I'm more familiar with the 88-94 stuff as that's what I used to race flattrack with . Each year the intakes seem to point in a slightly different direction so getting the carb to the intake boot or to clear the rear shock can be an issue. But for the most part Yamahas are like Lego.

[SmokinRZ]

Yamaha had two year development cycles, the 84/85 were mostly the same and then the 86/87 were mostly the same as was the 88/89. As long as the intake has the right angle they should all bolt up.

I had a 85, 86, and then a 89. The 85 had nice wide flat powerband but didn't really have a top end hit. I loved it. The 86 hit like a 125 and I hated it but the suspension was a lot better. If I had the option, I would use the 85cylinder unless you like the hit of a 125. The 89 was real nice down low and also had a nice hit and over rev on top. Progress.