I have a Jacobsen Mower with a D950 engine in it. It is hard to turn over trying to start. It acts like a low battery, but battery is good. Cleaned all cables still the same. I have another just like it so I switched out the starter motors, still the same thing. The battery and starter from this one starts the other just fine. Its almost like it has to much compression. I pulled the glow plugs to release the compression and with them out its still the same. Any Ideas would be greatly appreciated. Thanks