Excesssive popping when decelerating

[eddy314]

79 Carb with 1800 head and Weber 32, recently started to "pop" and backfire when decelerating or downshifting. Any ideas?

[So Cal Mark]

exhaust leak, faulty air injection or overly rich mixture or a combination of all 3

[majicwrench]

Mark is right of course. TO pop in exhaust you need fuel and air. Take away either one and no pop. Air gets in from exhaust leaks, air injection, or cylinders that don't burn well. Fuel gets in from cylinders that don't burn well. All factory carb setups have some sort of decell device to keep the throttles from slamming shut when you let off the gas, closed throttle hard decell will run way too rich and cause fuel to get into exhaust.
Good luck

[courtenay]

My '80 Fi does the same thing. What might cause this on a fuel injected engine?

[pooldoctorstl]

Same concept on FI cars. Check the throttle position sensor adjustment because one of it's functions is to shut the injectors off while decelerating to prevent this condition. Most manuals should explain how to do it or get Brad Artigue's manual at http://www.artigue.com.

Jeff

[eddy314]

Follow-up: Suprisingly, backing out the idle mixture screw 1/2 turn solved the problem. Thx