I bought a late 90's Exmark metro 36" mower about a week ago, everything seemed fine when I ran it around at the previous owner's house. After using it a few hrs the other day I started to notice it jerking about every 8 secs while mowing. It feels almost like what a stick shift car would feel like if you pushed the clutch in while going down the road then dump it. Its like it loses power from the belts for a sec then catches and jerks and pulls like normal again. I've never seen a problem like this so I was hoping someone on here had seen this type of problem before out of a belt drive walk behind. Thanks in advance.