200 degrees really isn't that hot. Especially on a hot day. But you may have 195 degree thermostat. If so you can drop down to 180 or 160 degree thermostat for that engine and get it a little bit cooler. I've run 195 thermostat in my old 235 in the past with no issues.
In addition to the others good ideas, make sure the gas cap is vented. If not you can pull a vacuum on the fuel tank and it will quit running.
An easy test for that is to simply remove the gas cap and go for a test drive.
