I have been quietly lurking here for several years and have benefited greatly from the combined knowledge base. Thank you all for that!

I Had my DAR inspection last week and received the A/W Cert. for my KF5/7FWF.

The engine, a 912ULS, has several hours on it from ground runs and slow taxi tests. But I’ve never run it much over 4000 rpm (Ignition check). Carbs are in cinc and It runs smoothly from idle up through 4000 with a good ignition check.

However, at 4600-4800 it stumbles and rpm’s drop to the 3k range with rough running until you throttle back.

This was two days ago and I have not had time to look into it beyond pulling the upper cowling.

My thoughts- mixture leaning out due to something in carb?
Spark plugs?
Ignition wires?
Excessive oil K&N air filters?
Intake air leak?

Any suggestions before I start taking things apart?

Thanks,
Todd