I had some starting issues also. Mine would crank slow usually so I bought new batteries. That didn't fix the problem and finally one day I went to start it and it went "click". The lights inside dimmed a ton like the batteries were dead. So I had someone try to jump start me and it still wouldn't start. I ended up connecting the jumper cables directly to the starter and it finally started.

When I got it home, I used my jumper cables to try to isolate bad wires by connecting it from the starter terminal to the battery. Tried to start it and nothing. Then I connected them from the frame to the engine block and it fired right up. Turns out my large ground cables between the engine and frame were worn and no good. Replaced those and have been great since.

 

Excellent video> Completely Rebuilding Your Starter