ORIGINAL: nmking09
Bad mounting job, these are not toys. It really looked like a harmonic oscillation break, induced by an extremely rigid mount. It has convinced me to purchase some stand offs instead of using the supplied mounts.
Xoar 22x8, lawn boy oil 32:1, 40deg F, 300ft ASL, and 7200 rpm.
Never solid mount any engine to a bench! That was crazy.
John