Mixing old and new piston rings

The title says it all - like having a new cast-iron ring and a old
chrome ring installed at the same time. The chrome ring is pretty well
worn. My gut tells me this is a bad idea. It's a 1982 Yamaha DT80. Will
it damage the bike or just run like crap? Thanks!

 

Yep. What Jack said. Why even bother without both rings?

 

I had broken two pairs of the new chrome rings already and this was a
last-ditch effort to get the bike running. I found out later that there
was still carbon in the ring grooves.

 

I do have one more pair of rings on the way and just wanted to know if
it would damage anything to run the bike as it is now.

 

wait for the new rings

 

I used a wire brush to clean out the crap, but I used a brass brush.
Would that still damage it? (I knew steel would mess it up)

 

After I used the brush the surface still looked smooth and unmarred.

 

Brass is soft, won't damage the aluminum like steel. If you want to see
if the ring grooves are wider than they should be, check your owner's
manual and find out what thickness the rings are and what width the
ring grooves should be and use a thin feeler gauge to find out what
clearance you now have between the rings and the grooves...