just got this

Was red fork boot OEM

Is that a 78 400?
looks like a great buy at $400.00
Newman who post here a lot can help but I thnk he is on vacation right now.

'79 YZ250F? I loved my 250F. Hopefully it's not the '79 400. One year only engine design. Pistons are almost non- existent for them.

That is real sweet slomoto.

I'm happy for you, finding a bike with memorys is great + it's good looking, even greater,
a big smile and have fun.

Lever looks like a "dehandler", hot setup back in the day.

Try ebay for parts or vintage swap meet

Try ebay for parts or vintage swap meet

For OEM parts, always check with the dealer first. You'll be surprised by the amount of stuff that's still available.

Looks like a 79 to me. I bought one late last fall. Just now getting around to restoring it. Still has the original piston in it. Sat around unused since 1982, or so I was told. Got it from the original owner. Plastic is really hard to find, fenders in both yellow and white can be had and some cheesy side number air box covers, but nothing close to stock. Tanks can be found on eBay, I have 4 in my garage right now. Pretty sure the stock fork boots were black, but not positive. Oddly enough the bike I bought was also running #8 on the plates.

http://www.x-tremevintageyz.com/index.php

http://www.backinthedaymx.com/home.html

http://www.amsracing.com/

http://www.vintageiron.com/

http://www.dcvmx.com/

As CamP recommended, try Yamaha first for OEM parts. Still quite a few parts available.
On the '79 models Yamaha moved the swing arm pivot closer to the countershaft to help eliminate thrown chains. A bad habit on the '78's. They also replaced the spring loaded chain tensioner with a stationary unit. Transmission ratios were changed between the '78 and '79 along with a different shaped head and lowered exhaust port. Most of the changes between the '78 and '79 restrict part swapping between the two models so the '79 is basically a one year model.

There's someone selling an ignition set up on Mark's swapmeet that's supposed to help with the pipey power delivery of the '78-'79 models.

To help a little in the brake dept. you might want to pick up a dual cam front brake plate from a 1980-81 YZ465 or 1981 YZ250. Those versions have the brake tab located in the correct orientation to match the fork leg on the '79.

The forks on my '78 were designed to run with 10-15 psi of air. Not sure about the '79. I would have someone look at rebuilding the shock soon. Manuals turn up on Ebay on a regular basis.

It is almost universal for all damping rod forks.

120mm (from the top) best bottoming resistance.
130mm
140mm
150mm softest setting.

Probably run 20 weight oil. Although those forks are going to be pretty mushy. You can run straight 30 weight motor oil if needed.

I think those forks are KYB's, 38mm tubes. You could probably get a set of stiffer foork springs through Race Tech.

Looks like a fun bike!