You might want to get a good load test on the battery. These 6 volt bats. don,t sell very good & sometimes have been in stock a long time. I,ve had that happen before & changed bats. & it whirled over. Is the neg cable hooked to the engine or trans. Sometimes that works better then going to the frame & then the engine. Could be the engine is tight from setting. Carbon or rust on the cylinder walls.
