Afterfire pop?

[rickf]

A backfire on deceleration is usually caused by a leak in the exhaust system close to the engine. Exhaust manifolds on these leak a lot but the one that usually causes the backfires is the gasket between the manifold and the front pipe. Leaning out the idle mixture is sure to give you the infamous M-151 flat spot at cruise speed.

[Husker]

It may have been an altitude thing I never had it occur beside the few times..... when I drove to work I don’t get it. But I generally drive with a tiny bit of choke depends on the day.

[rickf]

The choke would just add to the problem if you have an exhaust leak. More unburned fuel in the exhaust and then you introduce oxygen into it as it comes out red hot and bang.

[Mark]

I think the accelerator pump adds too much fuel to for the engine to burn so the excess goes in exhaust system?