The #1 cylinder on my 4 cyl ZN700 exhaust pipe was reading about 100 degrees below the other 3. I cleaned the carb. Didn't help. I synced the carbs. That cyl was almost closed at idle and it needed syncing really bad. Didn't help the temp though. I ohm checked the coils, spark plug wires, and caps and they checked good. Finally, I changed the spark plug and that fixed it!!!! Your problem is the opposite since yours is running hotter than the other 3 but I thought I would tell my story just to say, sometimes the last thing you suspect is the culprit.