So it turns out my cam chain tensioner was fine, it's just when my engine (initially) overheated I also just happened to break the head off the nut that holds the front rack mount on & it caused some washers to rattle.
So, I changed the oil with what I had available (sadly, energy-conserving 10W-30) & thought all was done. Then I heard it slow down again. I pulled over (w/o stalling the engine) & idiotically opened the oil port again, getting sprayed with oil, again, but yeah there was smoke. So, I let it cool & went off on my trip again, the engine stayed running but I made sure not to go full throttle for too long at once & I made it home, another 15 miles north.
One thing I noticed was when I went full throttle past 35mph, the engine would surge after a few seconds. Anyone know what's going on?
1970-73 C70 Honda Service Manual: http://tinyurl.com/6ebwtw
1970-73 C70 Troubleshooting Guide:
http://tinyurl.com/6ebwtw (scroll to sec.7.1 page 101.jpg)
1980-83 C70 Honda Service Manual: http://tinyurl.com/hu42c
1980-81 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec.18-1 page 170.jpg)
1982-83 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec. 20-28 page 205.jpg)
1980-81 C70 Maintenance Schedule: http://tinyurl.com/z4zn6
1982-83 C70 Maintenance Schedule: http://tinyurl.com/hw35c
More resources for C70 Passports and Cubs: