Hello All,
I feel that I must weigh in, given I have used all three engine designs on my motorized bicycle.
First, I used a 5hp Briggs. I loved the vintage feel and the ability to build more hp, but I found that for stop and go traffic, which I find myself in, the Briggs would tend to smoke and also overheat.
Second, I used a Honda GC190. This engine is an OHC design. I loved this engine with its upright mounting orientation, but this motor did not love me. I busted about 4 to 5 of these engines, snapped valves, slipped timing belt, stripped timing belt pulley on crankshaft, and finally a thrown connecting rod. It was good while it lasted.
Third, I have recently installed a predator 212cc harbor freight engine, OHV design. This engine is THE ONE as far as I am concerned. I have not logged a whole bunch of miles yet, but what I have experience so far is more usable (low end) power, more robust and less prone to failure, and overall more reliable power plant.
I love them flatheads, but my heart says I have to vote for OHV with the Predator 212cc engine.
For what its worth,
Gilbert