UL912 Intermiddent engine failure

I rebuilt both carbs. The diaphragms are new and the slides seem to function as they should. The float height is, I believe set correctly, the floats are about a year old and float at the height of the pins, as they should.

Negative G's have an immediate effect, so I think that rules out a float problem. It would normally take some time to use up the fuel in the bowls. If the pistons were moving upwards with negative G's I think that would reduce the air velocity in the venturi and cause a lean mixture. But why no improvement with new diaphragms?

I do have another set of carbs that someone lent me to try. I have been hesitant to try them so far because I have the pressed on carb heaters and these do not. I would need to plug the coolant lines going to my heaters and pick a day when carb ice wouldn't be a concern.

I just heard back from Light Engine Services. They suggested sending the ignition modules in to get them tested and they are not functioning properly, so hopefully, problem solved. 

What was the end result?

Faulty ignition?