Ex500 - Sat for 2 years, has random "Slap" while trying to start

[chris_y2k_r1]

I recently picked up an EX500 in very good shape for next to nothing. It has been sitting for quite some time (A year or two). When I tried to start it up, while the bike was cranking - just on the starter, it would not catch, every couple of rotations I was getting a nasty and very audible "Slap". It can be felt on the cylinder. I put my hand on the bottom end and on the cylinder and it is definitely top end. I'm a bit curious (and nervous) about this. Everything on the bike is stiff from sitting so I am assuming that the wrist pin is just stiff and causing the skirt to hit the bottom of the cylinder.

It's completely random but does it more when initially trying to start the bike. It becomes less and less frequent but is more frequent w/ the throttle at WOT.

I'm an experienced mechanic for sure but I wanted to see if anyone else had experience with this specific symptom. I"m not looking for theories... I got plenty of those - I'm hoping someone else has experienced this exact issue - at start up. The EX is a 90, but I"m sure that any EX including the 250 is likely to have the same problem under similar circumstances.

Thanks in advance for any experience you can share.

ChR1s