Gary........check yer slanted radiator hoze fer incorrectly installed THERMOSTAT. (pointy end towards radiator) Don't have a thermostat???, don't know??? SQUEEZE the slanted radiator hoze fer a lump. While thermostats can malfunction, they're pretty bulletproof. You doubt? Remove the "lump" in yer radiator hoze and try running without thermostat. Won't hurt 'nuttin'.
Per yer description, it takes about 15-mins fer BLOCKED radiator hoze to cause engine to "burp" and spray water over yer weird squarecan 4-nipple frontmount dizzy. Make certain you have the rubber OVERFLOW tube installed down the side of the radiator, past the dizzy. Also, make certain ALL the gaskets are installed for the dizzy ........Dell, yer self-appointed sparkie-meister