Marc, these are all just shots in the dark. Things that I would use to attempt to find the problem.
How many miles do you have on it? Have you changed the oil yet? If so, did you clean all the metal shavings off the filter? Is you chain tight enough or too tight? Mine was making some pretty ridiculous noises when my chain was too loose and the ride was very jerky. If you have reached your first maintenance point, did you adjust the valves? When I'm warming my bike I get some strange clatter sometimes... and I think it's from the way I adjusted my valves. What kind of oil are you running in it. I would recommend a fully synthetic cause it withstands heat better and since the Zong is air cooled, it gets pretty hot and having synthetic well help prevent burning the oil. Are you over heating the bike, air cooled bikes don't like to sit and idle for a long time.
Like I said before, a few shots in the dark. I'll talk to some people I know and as you post more info on the crisis, I'll give them more info and we'll see where we end up.
950 miles. Yes I've changed the oil before and just did so again now. I cleaned the metal shavings. My chain appears to be of adequate tightness. I guess I don't really know what adjusting the valves means, so probably not.
Sounds mechanical, like a broken or loose gear. Do you think you ran it out of oil, was there any burning or heat? Could you hear which part of the engine or transmission the noise was coming from?
If you drain the oil, are you getting metal pieces mixed in?
There are a few engine covers that are pretty easy to access, and remove. I would start with the 2 on the right side, check for broken gears or shafts.
Maybe the starter motor went out? I am not sure how to check it, or even where it is, but I had that happen on a lawn mower once in a similar manner.
With the bike in gear, can you push it forward? Or start it by pushing it with the clutch pulled in and dumping the cluch.
It might have ran out of oil. If it didn't run out it was at least very low. It's hard to say where the sound was coming from. I drained the oil and didn't see any metal, but then again I didn't dig around in it. How do I check for broken gears or shafts? And I think the starter is back to working again. When the bike is in gear, I can not push it forward, which brings me to my next point; even with the clutch pulled in i can still barely move the bike.
So here's my current situation:
I got the bike home via a friend's truck and began to dig in. I drained the oil, added new oil, replaced the spark plug (which looked pretty bad. It was pretty black) and removed the air filter and cleaned it. After doing all this I tried to start it again to no luck. It's turning over but not starting.
When the bike is in neutral, i can push it just fine, when it's in first gear I can not push it at all. With the bike in first gear and the clutch pulled in, i can just barrrrrely move it. It's like the clutch is only partially engaged or something. I tried adjusting the clutch cable, but nothing I did had any effect on the 'partially engaged' feeling.
I'm at a loss as to what to do next. I'm hardly a mechanic but I'm willing to give anything a shot.