Vibration problem

That was the situation when I posted, yes.

However I've had another go and specifically set out to get vacuum balance at 2700. I have achieved this at the expense of a bit of imbalance showing at 4000.

However it's made no difference, I still have the worrying vibration at 2700.

Someone here suggested putting the prop in manual mode and increasing the pitch at 2700 to load up the gearbox and see if that reduced the vibration. I've tried that - it makes it worse. The gears have only done 70 hours from new so it shouldn't be gearbox play.

Another carb strip and clean next unless anyone has a better idea?

I guess I would take the carbs apart again and look very carefully at the needle, piston, and diaphragms, since the problem persists in the midrange.  Do you have a removable diffuser at the top of your main/needle jets?

I took out the main jet, mixing tube and needle jet. The diffuser didn't seem to want to move, I didn't press it. Are there different types? Carb is from 2006 I think. 

The diaphragms have only done 20 hrs from new (although 10 years old), they appeared fine. Needle and jets have only done 70 hrs shouldn't be worn. All looked good.

Pistons slide smoothly. Are they normally lubricated? They have black on them like oil with moly. Springs are undamaged.

I will strip them again in the next few days.

No real progress but more googling has found cases where vibration in this rpm band has been linked with corrosion or galling of the dog clutch ramps. Anyone here seen that happen, particularly at low hours? I think I'll have to strip it and look for my peace of mind.

Two LAA Inspectors have independently said they don't think it is serious and is ok to fly, so I have. All behaves well in t/o and cruise, just a nuisance on final and taxi.