Your carb either has problems or it may in fact be too lean. That can cause a backfire like that. Being too lean can cause you to use more fuel as well, even though that is counterintuitive.

If you do decdie to get a new carb, DO NOT get a 1407 or 1411 Eddy.

The other Eddy carbs should be fine, with the AVS versions being the front runners. You can rebuild the carb yourself with not much trouble. THe exploed view should be all you need. Most have a sheet showing how to measure a few things like float drop.