Sounds like you're moving in the right direction. I would have sealed the backplate and carb while it was out. You can try leak testing the engine while its running to see if it shows more leaks, but I seal all my engines from the start to just be sure. Carbs have been probs with these - pinch bolt can be tightened enough to crack body and let air leak when the throttle is pulled. These cracks are hard to see and find.

Takes 10 posts I believe.....