Aerovee Primary Ignition

[Holmesryan]

Yikes, i have been having primary ignition issues. I bought a plane that the builder threw in the towel and it has 77 hours on it. A little aerovee purrs like a kitten on the secondary but misses and backfires on the primary. I pulled the engine today, the witness hole looked correct. The magnet was correct. I put on new mags and tested to make sure the p-lead was grounding. I ordered new plugs and will ohm them before i install, what else should i be looking at. I am at a loss. Thank you all
Ryan

[Raluttio]

Check the clearance between the magnets on the flywheel and the mags. It should be .010” and is addressed on page 33 of the assembly manual.

Nothing else comes to mind - there’s not much that could be wrong with the system.

[Bryan Cotton]

Have you tried running it with the p-leads disconnected? That is worth a shot.

[Area 51%]

Wires going to the correct cylinders?

[Holmesryan]

I’m going to try running p-leads disconnected.

Then I’m going to change the top plugs.

Top mag runs to front top of engine
Bottom to the back top engine

The magnet I did not change but the orientation was correct with the s pole facing out attracting the north on an aviation compass.

[bvolcko38]

I had a problem with the primary. Kerry sent me a new magnet. It was identical to original magnet. The only way I could get the primaries to fire reliably was to close the air gap to .005"

[Murray Parr]

Wires going to the correct cylinders?

I think Area 51 is on to something here, plug wires going to the wrong plugs would cause the symptoms you mentioned. Easy to check

[Holmesryan]

Area 51 and others-

Top mag goes to front top cylinders should top wire go to x and the bottom wire go to x.

Bottom mag goes to the top rear cylinders, same equation as above?


Just as a follow up plugs all new, I checked and there is spark and I regapped the mags.

Re-grounded everything

Ran both mags p leads off, each time engine ran the same.

[Bryan Cotton]

Area 51 and others-

Top mag goes to front top cylinders should top wire go to x and the bottom wire go to x.

Bottom mag goes to the top rear cylinders, same equation as above?


Just as a follow up plugs all new, I checked and there is spark and I regapped the mags.

Re-grounded everything

Ran both mags p leads off, each time engine ran the same.

It sounds like you have the correct wires going to the correct plugs. It is sort of engineer-proof. The top magnetron will reach either set of plugs, but the bottom magentron will only reach the aft set.

Are you able to monitor all 4 EGTs? Or CHTs? Would be telling if either the front or back were good, and the other were bad.

I am still thinking it is either a flyweel index issue or a magnetron magnet issue.

[Area 51%]

Top mag goes to front top cylinders should top wire go to x and the bottom wire go to x.

Bottom mag goes to the top rear cylinders, same equation as above?

Just to be different (and the wires were so short they would touch the exhaust pipe) I ran the bottom mag wires to the bottom of the rear cylinders. It ended up working famously.