Going no where fast - possible tranny or sprocket issue?

[basic]

Here's my bike - 1980 gs750L

here's the short story - put new rear tire on, chain was probably to tight, went for a ride, 7 miles outside town bike breaks as I downshift to turn around to heaInfirmd back to town. When trying to go the motor just free spins, like there's no chain on it, happens in every great. Engine runs fine,will shift into any gear, but no go. After coasting the bike into a driveway, notice some smoke and the chain is slack, but not broken. haven't had a chance to look at it closely as it was dark. Bike does have a 530 chain conversion. Any ideas? Will post more info in the morning when I know more. Sorry about the undetailed post but I'm posting from my phone. Internet is down at home.

Any ideas and/or suggestions? Also may be looking for a good 1100 engine if this ends being junk. thanks.

[almarconi]

I'd remove the cover over the front sprocket and have a look to make sure the nut on the sprocket is tight. Sounds like the sprocket came loose.

[kichigai]

I'd remove the cover over the front sprocket and have a look to make sure the nut on the sprocket is tight. Sounds like the sprocket came loose.

I have to agree! Had that happen to me too a while back ago but without the smoke. Hear it's a common problem.

[basic]

That's what it ended up being. Think the smoke was from slight oil leak between head and block that leaked onto exhaust. Thanks for the replies guys.