Flyingfish wrote:
JP says I may have a mag timing issue – will check (again) next time in shop.
Have you tried an in-flight mag check ? This will sometimes point to one mag or spark plug being problematic when leaned.
The timing of the magnetos and resistance of the spark plugs also play a major role in getting a smooth LOP engine. You may want to try to time the magnetos using a modern digital device instead of the ‘flowerpot’. If you do a GAMItest at two different altitudes, John Paul should be able to detect any induction leaks.
MIchael: Yes I have done mag checks in flight no obvious issues for now.
Dirk: I have contacted John with your recommendation and he’s sent the inquiry to George.
No matter what altitude, the problem my GAMI spread is too high (4 liters) and the engine will not run LOP at an acceptable TIT.
Meanwhile I’ve found a very nice workaround with a 60% ROP setting which is smooth and burns “only” 70 liters for a TAS of 189-190 at altitude.
Update: just finished a 50 hour. Yes, been flying a lot. And enjoying!
We checked mag timing and found one at 20 degrees and one at 22. We set 20.
TIT is lower now but still no joy with LOP – too hot or too rough…
I found a slightly damaged rubber insulator on the cable near one plug.
Taped it over. Is this a major issue?
A bad HT lead would not help to run LOP.
Retarding the ignition would increase rather than lowering EGT
You need to reduce your GAMI spread. 1 gph is too much. I seem to remember you could not do the test because you had some faulty probes, but you have surely fixed that by now.
Aviathor wrote:
Retarding the ignition would increase rather than lowering EGT
Agreed… and yet… very happy with the lower TIT . Go figure…
I am working with GAMI on the LOP thing.
I’ll watch the behavior of the cylinder with the damaged insulator. it is #4.
I had to replace several ignition leads (arcing) until I switched to Tempest spark plugs. The previous Champion spark plugs had too high resistance and the ignition current was taking shortcuts and arcing in the leads; no more arcing since the Tempests.
The crappy Champion plugs have destroyed magnetos too, because any increase in the flashover voltage of the load (the spark plug) translates directly into the magneto (and harness) insulation having to withstand the higher voltage.
I worked in high voltage in a previous life, up to 500kV DC, 1ppm stability… fascinating stuff 
Worth checking the breakdown voltage of 11mm at FL200 :)
