Yes, it will spin the engine no problem with the glow plug removed. As soon as I put the glow plug in and the engine has compression it can't spin it past the compression point. The battery is probably about 5 years old. I have another dry cell motorcycle battery that I hooked up to the starter and I have the same issue. I even tried another starter and the same problem. However, this morning before heading out to the field I tried starting the engine at my house and it was able to turn it. But the engine was at room temperature. Seems as soon as I head out into the cold the engine becomes more difficult for the starter to spin. Almost like the cold temps make the head shrink slightly which causes more resistance perhaps?