That brings back memories! I ran a saw setup like that as kid back on the ranch! Looks dangerous now but man was that saw fast!
During this years Homecoming we ran a buss saw like that using the rear wheels of a Model T.
Sawed for years with rig like that powered by Hubmobile engine. Pulley was bolted to the flywheel.
Here's a picture of a much older Bud Merz and his buzz saw in action:
This guy is big into safety, even the "Sealed for your protection" sign has been tossed aside.
It has an "engine fan governor". A similar one was discussed about a month ago on one of our doodle-bug threads.
A piece of sheet metal in front of the fan is held forward by a spring. The desired engine speed causes the fan to pull the sheet metal back. The linkage is rigged to hold the desired speed with the sheet metal pulled back. As wood is fed into the saw, the engine slows, the spring pulls the sheet metal forward, the linkage opens the throttle, the engine speeds back up. Crude, and not very precise. But amazing the ingenuity of that generation.
Great photo! Thank you Jay!
You may say that governor is crude but there's a decent chance your lawnmower is governed the same way, except the paddle is moved by the cooling fan's discharge air.
It's only unsafe if you get your fingers in the saw. I have cut many slabs with a pto driven cut off saw that mounted to the three point hitch on the old 9n ford. Still have all my digits. KGB