Petcock not functioning

[Popeye]

Hey ya'll, the petcock on my 84 250r isn't draining. I took it out, but haven't really looked it over. Any ideas on why it isn't working? Could it be clogged? If so, how would I go about unclogging it? Any suggestions? It's holding fuel in, but not letting fuel out when opened. If I bought another one, what years or models will interchange?

Thanks

[yamaha driver]

you could try an aircompressor i used it on my yt 125. I left the gas hose on the petcock, shoved the air nozzle in the hose turned the petcock on and let it rip