My first question would be is the oil level hi? If so, does it smell like it has gas in the oil? Fuel will overthin the oil, raise the level and cause smoking.
I use Pennzoil 10W 30 year-round. Synthetic is a waste of money and not recommended on a new small engine. Synthetic can actually delay piston ring break-in.
A puff of smoke on a new engine at startup is not uncommon but should go away after the first 25 hours of break-in run time.
If it continues, there is a problem with the valve guides or the piston rings.
20W 50 is used in larger automotive engines and too thick for small engine.