Popping or Backfire on shifting?

[DaddySS]

What causes popping or slight backfire on shifting - too rich or too lean? Or other, this is primarily when shifting (manual) in the 2500 to 4000 RPM range, a slight pop when letting off the gas.

[Happy Jim]

My first thoughts would be that you've got an exhaust manifold leak (slight) that's letting air in on the overrun.

Rgds

Jim