7.4L Thump/misfire/backfire during plane

[Alvie]

Last two times out I've experienced what I would describe as a thump and split second loss of thrust as I plane off leaving the marina. Each time this has happened, I immediately throttled down and all seemed normal. Then I hit it again and it planes of and runs with no issues. Just guessing that it is possibly a misfire or backfire. Anyone experienced something similar and know what it could be?

 

[AllTideUp]

When was the last time you changed your spark plugs, distributor cap, spark plug wires?

 

[hottoddie]

Sounds ignition related as atu said. Does this have a carb, efi or mpi fuel system?