[mr. softie]

I had similar problem when I first got my gz. It had been sitting. Would not run without pumping throttle. Backfiring like crazy. Tried stuff in gas. I "sort of" cleaned the carb three times. Finally I *!completely!* disassembled carb and soaked all the jets etc. including the body (after removing all the rubber parts) in straight carb cleaner (gumout) overnight. Pay attention to the idle mixture air screw. There is an "O" ring down in that tiny hole. You must remove it and all other plastic and rubber parts or the carb cleaner will ruin them. There are tiny passages in the body that get clogged up. Soaking is the only way to clear them.

This worked. I blew out all the passages with compressed air. Checked float level. Reassembled carb. Installed and really tightened hose clamps holding the carb. Like new bike now.