Outboards arn't my bread and butter, However two stroke chain saws are. On a saw 160-140 Is new, 140-120 is used in good shape, 120-100 is still usable but much reduced proformance. And anything under 100 is bad, Cant keep plugs clean, smokes alot, hard to get started, will stall much easier, and way reduced on power. Note, Most outboards are two cylinder and chainsaws a single. I do know a saw will not run under under 85psi and is super hard to get started under 95 psi, Once you get the piston rings and cylinder up to temp it will pop but that may take 20 pulls of the cord. Just keep in mind this is my experance from two stroke singles, A twin will be slightly different. A motor running 90 on one piston and 100 on the other should run fine after you get her going, just won't be long till a rebuild.