Thermosyphon cooling doesn't work too well in Florida. I have had two 4/4s Climax and Standard engined (still have it). I also have a Matchless Trike.
I believe the temp of the air and that of rad is too similar to get good movement and hence the lack of cooling. Only when everything is perfect, will it work, and that situation is fleeting. Live with it or install an inline water pump (and most likely, an alternator.)
Cheers,
The engine should be running at about 90C which is to say maybe 200 in F. I've been to Florida - its warm but not that warm.
All a thermosyphon needs is that the top of the radiator is higher than the top of the engine block in which case the hot water at 90C will flow from engine into radiator and colder water at the rad bottom will flow the other way. Basic physics.
Sure a pump will help, Leaving aside issues about engine performance and air petrol mixture, the cooling issue is whether the flow through the rad is sufficient for the dissipation of the engine heat in Florida weather. An old clogged radiator or air locks or kinked water pipes etc could limit the flow
