I have a stock water pump and have tried everything from a plastic flex fan rated at 8000 RPM, a stock fan, and am now running a 6 blade high-defection steel fan. I have built a fairly good shroud around the fan. The only thing that I have done differently from my last motor is changed the jets in the carb to smaller ones. Would changing the jets increase the heat enough to make a difference, or how about my timing, I run it at about 35 deg advanced.

What do you mean by a racing thermostat?