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Balky IO-390-EXP

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Engine conundrum: IO-390-EXP (RV-14A) with bilateral pMags. 200 total engine hours (problem free): Unable to increase rpms above about 1700. Engine starts easily. Idles smoothly. Engine runs roughly above 1600 rpms, worse on one mag either side. Timing correct (5 degrees after TDC). Fuel injection normal, no obstructions. Flow confirmed to be equal in cylinders 2 and 1 (as control) using boost pump for 15 seconds. No induction leaks. New auto spark plugs properly gapped. Throttle linkages working correctly. Problem started with Lean Assist finding of slight lean on cylinder #2. Found arching on wire to lower spark plug #2. Replaced it with new wire. Problem got worse. All wires inspected and found to be clean and fully separated from other wires and metal contacts. pMags properly grounded. Stumped.
 
From what you say about the ignition, I would imagine that the problem lies there somehow. That said, I will just mention something so obvious I risk offending you, and I am 99% sure it is not the case, but this reminds me of one instance in my plane: I was doing a run up, about to take off, and I was alarmed at the sluggish engine and not being able to rev beyond 1500 rpm. A moment later I discovered that the prop was pulled toward coarse, so the little IO-360 didn't have the oomph to spin it fast in that configuration. Again, sorry for stating the obvious...
 
tom paul said:
From what you say about the ignition, I would imagine that the problem lies there somehow. That said, I will just mention something so obvious I risk offending you, and I am 99% sure it is not the case, but this reminds me of one instance in my plane: I was doing a run up, about to take off, and I was alarmed at the sluggish engine and not being able to rev beyond 1500 rpm. A moment later I discovered that the prop was pulled toward coarse, so the little IO-360 didn't have the oomph to spin it fast in that configuration. Again, sorry for stating the obvious...
Click to expand...
tom paul said:
From what you say about the ignition, I would imagine that the problem lies there somehow. That said, I will just mention something so obvious I risk offending you, and I am 99% sure it is not the case, but this reminds me of one instance in my plane: I was doing a run up, about to take off, and I was alarmed at the sluggish engine and not being able to rev beyond 1500 rpm. A moment later I discovered that the prop was pulled toward coarse, so the little IO-360 didn't have the oomph to spin it fast in that configuration. Again, sorry for stating the obvious...
Click to expand...
tom paul said:
From what you say about the ignition, I would imagine that the problem lies there somehow. That said, I will just mention something so obvious I risk offending you, and I am 99% sure it is not the case, but this reminds me of one instance in my plane: I was doing a run up, about to take off, and I was alarmed at the sluggish engine and not being able to rev beyond 1500 rpm. A moment later I discovered that the prop was pulled toward coarse, so the little IO-360 didn't have the oomph to spin it fast in that configuration. Again, sorry for stating the obvious...
Click to expand...
Your "obvious" idea was correct. Embarrassingly simple.
 
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