Popping when decelerate

[Boomer123]

I get a popping sound when I let off the gas when shifting gears or pull in clutch to come to a stop.

[Jims99]

Stock exhaust? Desmogged? It's probably a vacuum leak. After market or modified exhaust will do the same.

[Mooskee]

If the backfiring just statrted, and you haven't made any changes, it is most likely a vacuum leak or exhaust gasket leak. Exhaust gasket bolt torque is only 7 ftlbs, so be careful or you can break an exhaust stud.
For finding a vacuum leak you can use some starting fluid spray. With the engine running, spray it on each the vacuum hose connections under the carbs. If RPM increases that lication is your vacuum leak.
If you changed your exhaust to an open exhaust like Cobra 6 into 6, it lowered the back pressure and the engine is running lean. You might be able to tune it out. I just rejet.
If it has been sitting with ethanol fuel in it, the slow circuits are plugged and causing a lean condition.

It could be a failed Air Cut Valve. Generally not repairable without breaking the carbs apart.

Let us know what yourspecific situation is, and we can probably help you fix it.
Dave