Hello I got this riding lawn tractor and I am having trouble getting it to start. The problem is it cranks but very slow like the battery is weak and doesnt have enough power to spin the engine fast to get it started. The engine is a briggs 26 hp. There is no load on the engine, the deck is off, and the engine spins easy. I could rope start it no problem. I tested it with 3 different batteries all I know were good and I get the same result every time. I even bypassed all the electrical and hooked the battery up directly to the starter with the same results. I took apart the starter and cleaned it up and made sure all the connections were solid and the brushes where good. Is it possible for a starter to go weak? Is there any tests I can do on the starter? Thanks for any help.