As I alluded in the "Milestone" thread, I have been chasing an ignition problem in the Mangy Fox ever since the first start. Because of this, the flight testing has been put on hold.

Here is a description of the problem:

On doing the run-up to 4000 rpm, testing one ignition (A) will drop about 50 rpm. Perfect.

Testing the other ignition (B) gives ~500 rpm drop and the EGTs (located on cylinders 3 & 4) quickly climb through 1500º! Not so perfect.

I have done all the usual stuff.
  • Cleaned all grounds
  • Checked firing order
  • Cut the tips off the plug wires and inspected boots
  • New Plugs Gapped to .027"
  • Removed modules and checked wiring
  • Removed, cleaned, rebuilt, synchronized carburetors
  • Then I did it all again...


I spent time today speaking with tech support with CPS, LEAF and Lockwood. The guys at Lockwood cam up with the theory (and they have seen this before) that one of the modules is malfunctioning and could be firing one side 180º off. This would cause the problem I'm seeing.

Each module fires a coil every 180º of crank rotation and each coil fires a pair of plugs (1 & 2 top, 3 & 4 bottom, etc.). If the module is malfunctioning and firing both coils at the same point, then one pair of plugs will ignite the fuel on the way out the exhaust valve, causing the EGTs to skyrocket.