I have one of the IR temp guns - where do you measure, and what's the upper limit of "too hot"?
You also say:
Not sure I'm hearing the four-stoke signature with my ear.
When I'm using using the IR I have a big log down and aim the IR at the chainsaw's jug while the saw is loaded in a full bar cut with a sharp chain and I want the saw's engine to stay loaded up good in the cut for several seconds, enough for the jug to reach a max stable temp and not exceed 350. If it heads for 350 fast it's going to Over heat. You can do this by yourself with a log down and letting the chainsaw do the cutting W/O forcing the saw if the chain is sharp. I have several post's (not threads that I've started) on this site about such. My searches did not find them. A tach in a full bar cut would have the engine rpm's lower than max spec's with the engine loaded and seem ok, but the engine's block can be overheating when loaded due to number of reasons, but mainly not enough gas hitting the piston (leaning out) and the piston's skirt starts swelling into the cylinder FAST and and producing more heat and eating itself. The OP if not familiar with such will think the saw's chain is bogging down, not realizing it's the piston's friction, lift the saw out of the cut, piss rev's few times and when it picks up throttle rpm's, he jams it back into the cut and starts repeating the act of destroying the saw's piston/cylinder.
Here is some info and a link to tuning by ear by bsnelling that is good.
AND IR temp of chainsaws using a IR theromometer
Nominal OK temp 350F if reached slow in in a full bar cut.
If the temp is rising fast and gets to 375 headed for 400 take it out of the cut and let the engine cool down to 350 or less before killing the saw. Do not kill it when hot or it may continue overheating or won’t cool off fast.
Tuning a chainsaw video by bsnelling.
Very good.
https://www.arboristsite.com/community/threads/chainsaw-tuning-101.250802/