912 excessive RPM drop on lane A

Garrett thanks for the reply. I did swap the six pin connector and The four pin connector both tests the problem stayed on the same side. I I have never seen the notes below about the charging stater red wires and grounds I will check them tonight. Did I test the coils correctly? The book says to test From primary coil wire to ground. I have tried that and I don’t get a reading on all four coils.

Maybe you have a broken wire under the insulation, use a needle to prick thru the insulation under there wire close to the coil. It sounds like you are zeroing in on the problem. Maybe it's a bad coil or wire coming out of the coil.

Hey Garrett, I’ve got spark on all spark plugs when the mags are on. Wouldn’t that tell us that the primary side is working OK?

 Yes it does. After rereading your initial post is this how the ignition wiring is configured? ignition circuit A: 1-2 TOP 3-4 BOTTOM. ignition circuit B: 1-2 BOTTOM 3-4 TOP 

Are you checking each ignition circuit at 4000 rpm?          

As a final check to verify the carbs are balanced have you pinched off the rubber hose on the balance tube and verified they are balanced? There should be no noticeable change in engine speed or vibration if the carbs are perfectly balanced.

 

 

yes my ignition is configured that way maintenance manual 74 Dash 00 Dash 00 page 27 figure 74–19 with one pen, four pen and six pin plugs. My mag checks are always done at 4000 RPM. I will Pinch the balance tube and see what happens. I bought a carb mate balancer has always worked for me in the past., I have a couple other things I want to check, bear with me. Maybe a day before I post again