On Dec 23, 4:13*pm, jim wrote:

If this thing is designed to have a large inertial mass attached on the
other end of the crank then that could be aggravating the kick back
also. But usually a horizontal 5hp would just have a small pulley to
drive a belt.

-jim

Horizontal engines usually have a substancial flywheel / blower. Some
vertical engines used on lawn mowers have a lighter flywheel and
depend on the blade to act as part of the flywheel.

Dan