I am put a new 14.5hp briggs and stratton on my ZTR, I bought it brand new in the box. When I first pulled the motor out of the box I checked the oil and there was oil, how ever...it looked bright(neon) yellow, I hooked it up and started it ran it for about 20 seconds, then tried the left wheel lever, and the motor quit; it sounded a bit like the belt was slipping. I pulled the belt off and now it is very tough to turn the engine over (using the recoil). So tough that the engine will not start. I checked the oil and there was none on the dipstick....what the hell. Before I started it....there was. I added a full liter just to bring it up to full. What did I do? What could be wrong?