I had the same problem with mine, prev owner knew about the problem so he disconnected the temp light sensor wire from the switch on the head.
I found out after I managed to get it running, the spark plug was faulty so i could not get her stared when I purchased it, opened radiator and could not see the coolant circulating.
I tore into the engine and found that water pump casing was missing the bearing the balancer shaft bearings where shot, crankshaft bearings shot, front case bearing on magneto casing fell apart trowing ball bearings into the case, chewed up both gears, snapped water pump shaft on balancer, counterbalancer was no longer spinning due to shreded gears so no oil pump.
Lucky for me cylinder and piston was not damaged even with all these issues.
Just waiting on parts to do a complete rebuild.
At least I managed to get it cheap as he could not get it started.
I hope yours is not as bad as mine was.