If the engine really is running too hot and you haven't been misled by the melting rubbers, then with an old bike it's much more likely to be due to a fuel supply problem, IE weak mixture. Check tank vent, tap filters, fuel lines, carb jets, float valve and passageways, etc. If that doesn't sort it then check the ignition timing (too advanced) .
If it's smoking it's getting oil, overheating unlikely to be due to lack of oil, it would quickly seize.
I'm not familiar with the 175 pump but the check valves stop oil being pushed back into the pump by crankcase pressure. Pump internal construction may stop you sucking oil from the outlets.
There were two types of check valve used on the 175, see Graham Weeks pump rebuild guide on this site for more info. Maybe one of our members can post a link. Brian