Not crazy about the 4.8v plan (prefer 6v+), but it should be OK, especially if you're OK on top end. If the voltage were sagging, it would go into limp mode, and never deliver more than about 25% power, while sounding like it's got a major carb issue.

From what you're saying, my bet is you're too lean on the low speed. That engine should flip start easily. The fact yours is balky even with a starter is a big hint.....

The richer low speed setting will force you to open the throttle a bit to maintain idle rpm. Doing that increases the airflow over the tiny idle jets in the carb bore, which will effectively make the engine noticeably more forgiving where you are having trouble.