Did ya clean your air filter recently? Paper filters can and do get choked with debris. I don't like cleaning paper filters, I believe that doing so damages the paper. But, you can just blow it out with an air compressor, see if that helps, then order a new filter if that WAS the problem.
I got mine here: Honda CX500A C D Z 78 82 GL500 I 81 82 Air Filter 12 91100 | eBay