Just curious, did you check oil level on lipstick? Maybe if it's obviously high, definately a red flag. Not sure how long you've been tweaking it, or short run/stop cycles, or hard starting,...ect? Could be a combination of any/all of too much dumping gas down carb, too high pressure overcoming needle/seat, bad diaphragm, on top of old oil.
Start with basics! Fresh oil. Tune to where it starts without priming carb every time or cranking it forever.