Montgomery Ward Riding Mower Won't Start

I have an old Montgomery Ward riding mower with a 14hp B&S that won't start. It has needed a new battery and I've been nursing the old one. It started after a dragging turnover and I let it idle while I trimmed the weeds. I shut it off while I push mowed the hard to get to places and came back to mow with it and it wouldn't start.

It was like the battery was almost dead. It would turn slowly until it hit the compression stroke then drag. I tried to jump it with the charger/starter and nothing. I went out and bought a brand new battery and same thing! It won't turn over fast enough. I pulled the spark plug and it looks good, and turned the engine without the plug and it spun really fast. Is this a starter going bad? I figure that once it meets resistance with the compression stroke, it just gives up. This mower is old, but just keeps going.

By Rick C from Mansfield, TX