The first few gallons, I put 5 through my 50, are simply for the breaking in and seating of the ring to the cylinder, the petroleum is a better oil for this purpose. After you get past the initial break in you can switch to the synthetic. In general the synthetics tend to be too effective at reducing wear and hence the ring will not seat in as fast, prolonging the break in time, should you run the Amsoil right off the bat.

Like I stated earlier the instruction sheet that comes with the engine will tell you exactly how to set up and run the engine from the first start up.