rough mid-range and carb questions

"...a richer mixture makes ignition work faster, so an over rich mixture could compensate for the additional advance."

I don't think there is a strong relationship between carb setting & ignition settings. 

There is another conversation, active at the moment, where the mystery roughness was eventually tracked down to old "O" rings in the carburettor (sloppy 5 year rubber replacement?)

I do figure I'll be compelled to rebuild the carbs, maybe when there's a forecast spell of miserably cold (by FL native standards) weather.  I'd probably throw the epoxy floats in too.  I have another engine on a test stand, and everything I need to make an EFI installation.  If that all works out I can bring both engines into this century :-)

Rusty

I had similar issue and it helped a great deal to move the needles to richer position. It was too lean. Worth a try ?

A few flying hours ago I installed a oxygen sensor in the exhaust  to try to pin down reason for slight vibration at cruise and I see the engine is still too lean from at cruise (low load setting). With AFR 15.5 I believe the vibration is misfiring from being too lean

I have KN filter pods and maybe this is the reason stock settings don't work in my case

New needle jets 2.74s and 2.76 are coming in and I hope the engine will be smoother with slightly more fuel

That's good info.  Thanks.  I've thought about installing a wideband sensor, but I'm trying to resist. 

I think I have more than one problem, and eventually I'll make some progress I hope.  The shaking is so bad that yesterday I found the two carb mounting sockets starting to tear apart.  I've also been watching a change in EGT from the last couple flights.  #3 and now #4 are both going lower, about 100F lower than they were just a few flights ago.  I thought for sure those torn sockets were going to be the reason, but I couldn't see an actual air leak from the tear, and after replacement there was no change.  

I did a short test flight today to test the ignition effect on EGT, and I can confirm that the A ignition seems to be the cause.  I can see the change on the in-flight tests when using just A vs B, but it's even easier to see on the ground. At idle, the #3 is maybe 100 low, and #4 is close to that.  When I switch to B, they all go nearly even.  I have another set of coils, and I'll install new wires on those, and maybe even new plugs (again) just to finally eliminate at least one problem.   Sadly, even with the "good" B ignition in flight, the engine still shakes like a wet dog 3500-4500 rpm. 

I also have two of the LEAF level 4 carb rebuild kits on the way.  If the ignition and carb work doesn't fix it, I'll consider trying a larger crossover pipe.  As a last resort, I'll send my gear box off to have it checked, despite only having 60 hrs since it's last service. 

Rusty

"I have KN filter pods and maybe this is the reason stock settings don't work in my case"

Air filters can only effect fuel mixture by causing a restriction.

Restricted air flow, from too small a filter/partially blocked filter, will cause an over rich situation ie the air fuel ratio will have too little air: fuel. 

Changing your carburettor settings, to accommodate a restricted air flow, will only result in problems later on (usually of the too lean variety).

If you suspect a filter problem:

Replace filter

Clean filter & re dress using approved materials & system (if a serviceable filter eg K&N).

If filter to small (this is really filter medium) upgrade to larger filter.