I have this same engine

About a gallon of 92octane with lawnboy 2stroke oil @ 32:1 mix

I was ruining a 17/6 falcon but chipped its tips to I threw on an apc 16-6. For a flight.

It has always ran well but for the last few flights its started running badly. Nothing has changed and its been on both props.

For the first half tank of fuel into a flight it runs fine. Haven't touched the needles out of the box. Its a bit rich on top and bottom but idles very low and reliable. Transition had a bit of a stumble but it clears out quickly.

But after the first half tank (4-5min of flight time) it starts to run a bit erratic. It will idle lower, so low it will die if not trimmed up a couple clicks. Top end full throttle has a little burble. It will run just sweet at midrange though.
And yet transition becomes awfull. Very stumbly.

Is it time to change plugs or time to start leaning it out? Or does it should like it has leaned itself out?