I picked up one of these saws the first of the week.
My back up saw was having issues, it was a 10 year old 52cc Chinese saw I got for free, then modded it to death, it never died but the crank seals were leaking causing running issues and the gas cap sucked so I scraped it. I had the larger 372 carb with a home made intake on it which is now on the joncutter.
I also put the 3/8lp bar and chain I had on the 52 straight on the 5800 and the gutted muffler so I didn't have to gut another muffler.
I tried to port the joncutter but one of the cylinder bolt heads is striped and wont come out so I didn't port it at all. If it needed rebuilt I could drill the bolt out but it seamed silly to mess with it just to port it. I checked the squish and compression, the squish was .045 and it had 175psi, it doesn't need much of a compression bump anyway. Also this saw is the 58 for sure not the 52, it has 34mm of stroke.
I put the bigger intake/carb on it and its way faster now. It cuts at 11500rpm now not 9000rpm, the max revs are only 1000 higher at 13500rpm but it doesn't drop down as much while cutting. Im thinking 90% of the gains on my 62cc timberpro were the carb/intake now, it also cuts at 11500 but has more power but it should it has more cc's and mods.
I'll post a video on the weekend.