I've been around long enough to have been involved in kart racing in the late 50's & early 60's, although I wasn't one of the "cool people". I had a Bug "Scorpion" made in Azuza CA that ran in class A Super. In those days we had classes like "A Bushing" for low powered 2 strokes like Clintons (5.8 c.i.) and a hotter class for engines like West Bends. "A Super" was for needle bearing engines - almost 100% McCullogh chain saw engines. These were 5.3 c.i. and much hotter than the Clintons etc. I never saw any B&S or other 4 strokes used for racing at that time.
My best "Mac 10" was hotted up to produce 11 hp @ 11,000 rpm. I used mostly a 9-1 gear ratio, with no transmission and no clutch. The kart had a solid rear axle with a single hydraulic disk brake (originally designed as a helicopter rotor brake).
A B-Super kart used 2 Mac 10's and a C-Super used 3. A B-Super kart produced competitive lap times at Lime Rock with E-Production sports cars (e.g. TR-powered Morgans). Faye Pearson, one of the Bug factory drivers (wife of the owner) was supposedly clocked at 90 mph at Nassau in her B-Super Bug. (Mine was probably good for 50 or 60.
We raced on road courses designed for karts - many were identical to each other. I also ran on dirt (~loved~ that) and a couple of 1/4 miles ovals.
I only have 2 photos, shown here.
Above - set up as an A-Super.
Above - B-Super setup. The kart had quick change sprockets (split, so they could be replaced without pulling the axle). These were useful to me especially since I bent so many spinning out into the mud.