Engine - Drivetrain

Does anyone know what this thing in the picture is? It appears to be in a fuel line?? A vent maybe??    

It ran good, not a real noticeable difference.  After mowing the last of my grass, I let it idle a bit and cut it off.  I tried to restart it hot.  It would not start.  I pulled the choke.  It started.  I pushed the choke off and it would idle and run fine up to about half throttle.  Over that, it wouldn't plane out and would puff kinda black smoke and run poorly.  It has done that on a number of hot start occasions in the past.   Oddly, one of my friends and his dad bought 2 of the exact same mowers with the same engine as mine at roughly the same time as mine.  They have roughly the same hours on theirs' and probably don't take care of them as well as I do mine.  They do not experience this issue.

Welcome mk please feel free to stop by the chat  some night

Right. But needed to be done I reckon. The gasket didn’t break on cyl no 1, the left one so I didn’t replace that one. Hope it doesn’t leak - really tight workspace there. I wasn’t too fond of how these valves adjusted. Just a lock nut where the rocker pivots and apparently the pivot is cammed. Not what I was expecting.    off to see if it runs differently...

That is loose but it won't help your starting problem.  Your problem is fuel starvation from overheating.