The missing head gasket could make the engine more prone to backfiring

A lean mixture will also cause back firing.

There is a mist of air/fuel that stands out from the basic carb body on the TT four stroke. This get blown around at times and the fuel is wasted. This deal about the mist sometimes getting blown away and sometimes not causes erratic and unsteady running in some installations. In some installations, it makes no difference about the choke body but in the ones where it does effect the engine, the choke body seems to contain this fuel mist better and makes the engine run more economical and steady.

Enjoy,

Jim