Engine Troubleshooting

[NilsWright]

Hi there!

As a first post here in EAA forums I have an interesting issue I'm working on.
It's about a Lycoming IO-360-A1B6 in a Cardinal RG.

It has a mag drop between 150 and 300 RPMs on the Right mag only. Left mag is 100.
This also means it will not develop full power. The engine will run smooth, however, there's no sign of a cylinder not playing along.

We have checked timing, swapped the spark plugs, ignition leads, magneto itself, ignition switch, to no avail. P leads were inspected and measured as well. Compression is good.
The intake system looks fine, external visual inspection, and the injector nozzles were cleaned and inspected as well, all fine.

Agressive leaning does not affect the drop as far as we could tell.

Does anyone here have some experience with similar issues?

Cheers!