What I typically do is look for basket cases that have as much of the original part stock as possible ... as well as some potential. You have to get these cases at the rock bottom price. Of course, everyone thinks their junk is collectible and worth a lot of money, but the reality is that you could take a total loss on a project like this if there's a fatal flaw. I mean, think about it ... the bike is in the state it's in because there is something wrong with it that likely originated decades ago ... and you have to find it!
I'm just wrapping the first phase of work on one of these old timers. It's a 1972 Yamaha LT2 100 that I paid about $100 for iirc. It was a Craigslist listing that said they had all the parts (many in a box) that turned out mostly accurate. The overall condition was extremely poor ... top end dismantled, stator exposed to the elements, and lots of rust from decades of outdoor exposure. This particular model and its condition didn't warrant any serious restoration work; there's not too much value in it, maybe $800 to $1000 in running condition. So the plan was to get it running and see what I could make of it without spending more than it was worth.
Here are some photos of what I started with:
The main thing I do before anything else is get the motorcycle running. Putting a nickel of money or an ounce of effort in a non-running motorcycle (other than getting it running) is a waste.
There's a simple formula that I follow in getting one of these bikes running. Stick to the elements of this formula and tackle them one at a time:
Air + Fuel + Fire = Combustion
Obviously in this instance the top end required rebuild. In rebuilding the top end I believe that I uncovered what caused the original breakdown. What I found was damage to the intake port in the jug that caused a very minor metal fragment to project inside the cylinder wall; hard to find until you run the piston/rings through it by hand and see where and how it's getting hung up. I was able to hone that out along with the rest of the jug and use a fresh stock/standard piston and ring set that I purchased off eBay.
Now the next question is how did that damage happen?
You do not want to fix something only to have the condition that caused the breakage to reoccur. In this case I can not be sure, but I have a hypothesis. These old enduros had 2-stroke with an oil pump to present oil into the jug behind the carburetor. In general, these pumps operated just fine, but improper maintenance rendered them inoperable. Most people didn't know that if you let the oil reservoir run dry, the pump had to be bled and primed or it wouldn't pump the oil. I'll bet that's exactly what happened because I got the oil pump working with little effort. This is the oil pump as it's situated behind a cover in the right side of the case:
I was getting some fits and spurts from the carburetor. It really didn't seem to dirty inside but I cleaned it pretty good, including an overnight soaking in acetone, and installed a Keyster Carb Kit. When I ultimately did get the bike running, I couldn't keep it running without the choke on. Round and round on the carb before looking elsewhere. Long story short is that I replaced the reed valves and then the whole reed valve block in the intake manifold and it started to operate fine for me.
Other than that, I spent a lot of time getting the stator back in working condition after being exposed for decades and the clutch seemed to come back to life with some fresh friction plates.
At that point, the motor went back in the frame and after a lot of tinkering around I got here going vroom pretty good.
The next step was cosmetics. As previously mentioned, the little bike doesn't have a great deal of value, so a full-blown restoration isn't an option. A full blown restoration would be either sourcing or restoring severely damaged/rusted/pitted parts, powdercoating applications such as the frame, replacing wheels and some nice paint. For example, both the cylinder head and jug have a cracked fin. In a full restoration, those would need replacement. In a simple garage restoration, if the part works (and ain't dangerous) = it'll be fine.
First was tackling the engine. I have a hand-held, Harbor Freight bead blaster that I use for cleaning and surface prep. Makes a huge mess, but does a decent job. Sometimes I can get cast aluminum surfaces to look really nice and be done with it; not the case here (no pun intended). I learned a long time ago that black paint covers a lot of scratches/dents/imperfections, so the case and jug got black and the cylinder head got painted aluminum (both high heat grade paint).
(see that broken fin? ^^ ugh)
From there it was part by part by part. First the part was studied to see if it would survive then it was blasted or sanded or whatever. Many of the parts were extremely rusted and pitted but overall I think I get the better end of the deal. Soft parts like brake pads, cables, harness, seat pad/cover made the cut. Tires had tread but had rotted so those were replaced and some new tubes were installed. Most all hard parts were able to be cleaned or blasted and painted. However, the spokes seemed a little too far deteriorated so I relaced the front and rear with new NOS spokes and nipples. While the wheels themselves were a cosmetic mess, they were solid ... remember my comment about black paint hiding all that? I painted the wheels black.
Another hard-to-refurbish hard-part was the shocks. Many years ago I purchased a spring depressor that makes disassembly easier, but they're still a bear to work on, especially in this condition.
All said and done, here's what the 1972 Yamaha LT2 looks like after I'm done. Beginning to end is about three and a half months. Actually I have a few connections to fix on the wiring harness and I need to find a 6v horn. However, it came out ... well, let's say ... respectable. Respectable from the stand point that the bike was brought back to life from the grave and will hopefully provide somebody some fun afternoons riding around in the Florida Sun.