Read about your temp test gun specifics. The measurement spot size is not the red dot from the laser. It is often a cone shape that fans with distance. Mine measures a spot size of 1 inch diameter at 1 foot from gun. The spot size increases with distance from gun. So don’t think you are measuring only the spot painted by the dot. And check if the laser is centered on the IR spot measurement area, as the laser is not centered in the IR detector, but rather in parallel, the cone and the beam will only converge at one point in the distance in front of it. The owners manual should explain where that point is.
Carb Rebuild kits have pretty loose dimension tolerances, and many have no quality control measures to find out of tolerance specimens. They leave those checks to the end user. That’s why many here seek genuine Keihin replacement components in order to keep four separate carbs delivering equal fuel ratios throughout the various throttle settings.
Since you have an engine that runs, nothing is going to scream “I’m obscenely bad”. The devil is in the details. As in finding what is different among the cylinders. It’s tedious. But without details, finding culprits without being there, is going to be pretty difficult. Particularly if questions or clarifications aren’t answered.
When I still had the airplane with a Lycoming 4 cylinder air cooled engine, the motor was instrumented at factory locations for cylinder head temperature. 300 to 375 was considered ideal operation @ 75 to 100 % power. During climbs with lower air speeds, 475 was sometimes seen. Before adding extra cowl flaps for more cooling air, I saw 500 and 525F for cylinder head temps. That engine broke off an exhaust valve head to rattle about in the chamber before getting chucked into the exhaust port (saving the piston from being holed). This engine was made to produce 150 horsepower continuously for 2000 hours.
When you took your temp readings, was there any airflow about the engine? And what was the air temp surrounding the engine?
Since you recorded uneven temps among your cylinders, you need to refine your measurements for faith in their accuracy, or start looking for differences in the cylinder mechanical operation or the 4 carbs operation differences that feed cylinders that you KNOW are mechanically equal.
Good luck!
