912 run rough on climb or heavy load

Don't use the old primer circuit. Stay with the enricher / choke setup.

Ok guys please don't dwell on the primer I already mentioned it was a test it is not connected to this problem. 

I wonder, could you have a cylinder losing a significant amount of compression at or above 5,000 rpm? A valve problem maybe? Did your differential pressure test change on a particular cylinder as compared to last year’s check?

           I assume a 'loss' of compression at 5000 could only be due to a sticking  valve or lifter. In my experience that usually manifests itself with a backfire of some type either through the intake or the exhaust. I will take a compression tester though and verify. Unfortunately I don't have power at the field so a proper differential test would be more challenging. I appreciate all the input though from everyone. I was looking for exactly this type of discussion and thoughts. I will continue to update this forum and will be making my way back to the plane on the weekend to focus on fuel related issues. I have new diaphrams for carbs and will weigh floats and then examine or remove and examine intake manifolds for air leaks. beyond that I fear I may have to involve a certified mechanic with spare components to begin swapping. I am really hopeful the endgame is not to have to pull the wings and transport back to my hangar for deeper inspections. 

I have been thinking about this issue for a while now. Jim's advice has some merit, I wondered myself if the hydraulic lifters could be holding a valve off its seat with higher oil pressure at those RPM's.

I still think the fuel flow is most likely the problem, most likely only one carb not getting enough fuel under high fuel demand situations. That would explain the shaking and significant loss of RPM.  Do you have a picture of your fuel lines, do they branch off like the ones in the installation manual. Perhaps a restriction around that area. 

Can you bypass the fuel filters and or Gascolator?  

Picture this; Your engine problem shows up under heavy load high fuel demand situation after about 5 minutes in this condition.

The fuel flow is almost keeping up with this but after 5 minutes one or both float bowls start to get too low from not quite enough fuel flow and the engine loses speed and starts to shake a bit.

At some point the fuel flow keeps up with this new slightly reduced fuel demand from the reduced load of the undersupplying carburetors but the fuel flow is not oversupplying enough to get above this condition.

One thing you can try to confirm this is to run the test and after the problem is present for a short while, reduce power to a light load for about 20 seconds (say 2500 to 3000 RPM) which should be enough time to refill the carb bowls, then reapply full power, it should then take a similar time to reproduce the symptoms. If the symptoms reappear immediately after applying the power, that suggest I got this wrong and the problem could be elsewhere.

Don't get too hung up on fuel pressure being good, I have a lot of experience with seeing good fuel pressure but not enough fuel flow.