By spinning gears, do you mean it is turning the engine over, or just spinning? I had a similar issue on one I bought recently and the solution was almost unbelievable.
Mine was spinning but making a grinding noise. I traced all the wiring, but actually found the leads to the starter (both hot and ground were on the starter) were reversed. The telling story was the lead from the starter relay, went to the mounting bolt on the starter, NOT to the side of the motor where the hot lead was supposed to be.
DOUBLE check your wiring BEFORE swapping leads. It might not be the case on yours. For the record, I have no idea why they were reversed but it was like that when I bought it. The seller advertised it as kick start only.