The radio noise is a clue I'm sure, but I haven't figured out what it means yet.  I don't see how replacing the resistor caps could have caused it directly.  The wire was clean where I trimmed it, and I marked the cable to know how far to expect it to screw in, so I'm sure they're well connected.  I start thinking maybe I dislodged a ground wire, or maybe pulled on the coil end of the cable where there might be a bad connection.  I did wiggle and pull on the coil end of the cables with the meter across the wires, and I didn't see any real change.  If I determine that the problem is in the coils or wires, I'll likely replace all the wires while I have it all apart.  I'll take another look at it Monday. 

Rusty

To be more specific about carb synch…. It is most important to match carbs at low engine speed (idle and off-idle).  Uneven pulses L-R cause gear chatter at low speeds and this leads to early destruction of the gear box.  Carbs need to be matched for manifold vacuum with the crossover tube blocked.  Mid-range and high speed are not adjustable.  Mid-range synch is a crap-shoot that you just live with it and avoid a rough mid-range as much as possible during flight.  Highspeed is matched well because of mass flow through wide open venturi of carb throat.  The gearbox will tolerate the mid-range roughness because the gears are spinning fast and prop loading overcomes gear mesh.  Idle is where the concern is…

Avoid operating the engine at idle speed on the ground.  Low idle speed is only used in the air during decent where prop is back-driving the engine and gear mesh is taken up in one direction to eliminate chatter.

On the ground, always keep engine at or above 2000 RPM.  Run at fast idle for engine start and warm-up.  I use 2500-2800 at start because engine does not run smooth until at operating temp.  This keeps the gearbox happy and that’s where you want to be for long engine life...

This was a double post and I can't figure out how to delete...  Sorry...

I agree with Mike F. you probably need a carburetor cleaning.

https://www.youtube.com/watch?v=Wi4v27UG-2Q

Thanks for the comments on carb sync, but I don't think that's an issue.  I suspected that, and had originally performed my sync at mid-range.  Just a couple weeks ago I re-checked the sync again just off idle as shown in the Rotax owners video.  It was essentially perfected already.  I tend to stay above 1800 in idle on the ground, and even that creates a lot of wear on the brakes. 

For those who think it's a carb issue, how does the carb know which plug I'm firing?  There is a night and day difference when I switch from A to B ignition.  Larger aircraft engines tend to foul the bottom plugs, so I can see the difference there, but the 912 doesn't really have that problem, and I recently changed the plugs so they were new.  I'd still bet money it's not the carbs.

If I can make it to the airport tomorrow, I'll start by swapping the 4-pin plugs to the ignition modules.  If the roughness moves to B, then the problem would be before the modules (trigger coils and wires).  If the roughness stays on A, then the problem would be after the ignition modules (coil, wires).  In that case, I'd put the 4-pin plugs back to normal, and swap the inputs to the coils for 1T-2T and 1B-2B.  If that moves to B, then it's the 1T-2T coil or plug wires.  If there's no change, I put those wires back and swap the 3T-4T with 3B-4B.  If there's no change there, I'll be looking for some carb cleaner, and maybe some seasoning for the crow I'll be eating :-)

Rusty