I have an 84 GSL. I still have to pass emissions test where I live. Last time they told me I had to mch un-burnt fuel in my exhaust. So I took it to a good mechanic who works for a local dealership. I had allready re-built the carb, but he checked it out for me. No problems there. He repalced the backfire valve. Found no carbon build up. I have had that problem in the past and would like to know more about carbon build up. Then he discovered that the catylitic converter was clogged, so he replaced that. Runs much better, but still has to much un-burnt fuel in the exhaust and won't pass EPA. My mechanic said it may be in one of the air valves on top of the engine. He suggested I attempt to flush out all of th lines in the Rats-Nest. Any other suggestions?