Rough running 912 during warm up

was this problem ever resolved? What was the solution? I have very similar problem and hoping to find a solution

From the description I would guess that you are set a bit too lean.  If it is rough from idle up to 2500, (2500 is a high idle) you should check the setting of the air mixture screw (factory setting is 1.5 turns open)  Inspect your carb needle clip setting, I would set it to clip position 3.  

What you need to remember is that the slides in the carburetors (pistons as you call them) showing rub marks, this suggests vibration.  Check that the carbs are not twisted on the sockets and the slides are straight up and down.  This is for the floats as well as the slides.  The sides are suspended on the "roller" diaphragms.  If you have marks on the sides of them polish them down with some extra fine paper, 1500 I would suggest, to smooth those areas.  i don't know the hours on the gearbox but perhaps it is in need of shimming to damp out such vibrations.

Cheers

Hi Ian & RW,

I just overhauled Ian's carbs two days ago.  I didn't see anything alarming. They were pretty clean except for the idle jets which I cleaned. His needle clips were in #3 slot on the needle. His mixture screws were set at 1.5 turns too.  No vibration marks on the slides and they were clean. His carbs looked in good shape. When you get the carbs back just do a good carb sync and see if the vibration has been helped. If the vibration is gone good and if not probably time to have the gearbox checked.

p.s.

When you reinstall the carbs make sure the center punch mark on the end of the choke shaft is pointing back towards the air intake or the molded pipe part of the choke housing. The choke shaft can be rotated 360 degrees and some owners accidentally get them turned the wrong way.

Like RW mentioned it may be time to check the gearbox.

It must be carb week. 😕😂  I have 6 more carbs to overhaul in the next couple of days.

Hi Roger and all

Just a note.  Bing stopped using a punch mark on the butterfly shaft in the past few years..  You will need to verify the angle cut on the butterfly itself to be sure it fully closes with the new ones. 

Cheers

Sorry, forgot attachment

Cheers