912 run rough on climb or heavy load

How old are the spark plugs, if over 100 hours replace as some may be intermittent under a load. Make sure all the plug wires are not touching the intake manifold.I’d check the balance the carbs at 5k rpm also. Keep an open mind and you’ll figure it out. Just my thoughts.

Dave, I will ask again, maybe I was not clear, how does your most recent annual differential cylinder compression test- by cylinder- compare to the previous test? And on a related note, could you have you recently inadvertently allowed air to enter the oil system?

Tangential thought - engine mounting rubbers???

Were they replaced at the last 5 year service interval?

😈