The engine manufacturer knows his product better than anyone else out there. It's always better to break in the engine his way. It keeps your warranty intact.

It wouldn't hurt to run the first gallon or so with an ashless natural lube. IF you can find an ashless oil. Because of exactly that, I've been breaking in my engines on all synthetic Motil 800 two stroke motorcycle racing oil at 40/1. The Motil 800 is a VERY high quality synthetic two stroke oil, and runs clean and cool.

Brison engines ARE supposed to be run from day one on a quality synthetic oil. The older Brisons were broken in on a natural oil then switched to synthetic if desired after the first gallon.

After the break in, I reduce the oil mix down to 65/1. After a couple of years of running the engines, the pistons and cylinders still look new. The engines have never fouled a plug unless I had the mixture set too rich. The bearings are still very smooth in the races, and compressions are generally better than the day I got the engines.

The engine manufacturer is going to look for excessive wear in the pistons and cylinders if you return one. Since most of our engines should last over 500 to 1000 running hours, the best oil you can get really matters.

By the way, non synthetic oils are much more prone to causing rings to stick. At any engine age.