Recently I hooked up alot of my emission parts to help pass the tail pipe test. With a bit of timing and air / fuel adjustments the carbed 305 passed with no problem. The only problem with this setup was loud popping from the exhaust after I let off of the gas anywhere above 3,000 rpm. The higher the rpm the worse that sound became. At 4 it would let out a bang before the pop. Playing around with lower gears would just sound nasty. I'm sure the engine was fine and the carb was tuned at the proper ratio from the emissions report.

After searching a ton of threads from google I only came up with answers of timing issues, bad catalic converters or people who say they actully like the sound. Yesterday I popped the hood and played with the timing. Advancing and retard none made a real difference so I decided to focus on what was going on in the exhaust. Mind you that I do have a Road demon 525 on a 305 that seems to run slightly rich ( not eye or nose burning rich ) from what my a/f guage says. Once it kicks down it runs as strong as a 305 can run. With that said, this setup was pumping the right amount of unburnt fuel and oxygen from the smog pump into the exhaust to cause it to combust in the pipes. As soon as I disconnected the air line that goes to the cat I could rev it up to 4 k with no popping at all.

Now I'm not saying this is the solution for everyone. Especially if you have a computer controlled engine in a state that is harsh on emissions. If you have this popping you might look into how much unburnt gas and air is being put into you exhaust. I'm sure my computer was meant to regulate the amount from the smog pump but it's probably very confused on my car since it detects half the parts are missing. I only keep it because it runs my speedometer. At any rate I'd say disconnecting that air line to the exhaust is a good quick test to eliminate the popping.