I just replaced all 8 last week
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PMag Spark Plug Guide
- Thread starter jliltd
- Start date
rexbrewer
Active Member
Tried Airflow Performance nozzles with .024" restrictors. No help. If colder plugs don't help, thinking dirt/disturbed flow in fuel servo????? Any other ideas?
Installing .024 restrictors doesn't change the nozzle bleed delta. Altitude and or velocity does.
Down low, cruise typically takes place with a partially closed throttle. Pressure in the manifold is low, while free stream pressure is high.
More velocity means more dynamic pressure, which shows up as higher upper plenum pressure at the bleed. A good ram intake and a wide open throttle will offset some, maybe all of it.
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Colder plugs will do nothing to improve or degrade general performance. An exception would be going so cold that there is not enough heat to burn off deposits and cause fouling, which will degrade performance. The goal is to be hot enough to effectively burn off deposits, but not so hot that the plugs erode or cause pre ignition. Beyond that, the heat range make no difference.
Please don't forget that the Autolite 373 spark plug is NOT a resistor plug. May cause some interference with an electronic ignition. The 386 is a resistor plug.
It should be noted that the L14-u is also not a resistor plug. I experienced no issues when changing and have EI. I do have to wonder if the 386 is also a non resistor plug. All the other autolites in that series are that way and wonder if the specs are wrong. Never measured one. I thought the 14U's may have also been mis reported, but those I measured as no resistance.
rexbrewer
Active Member
I removed GAMI injectors and tried Airflow Performance injectors with .024" restrictors. No change (except GAMI spread was greater and no longer smooth when LOP). Reinstalled GAMI injectors. Preignition? Will try DENSO L-14U (cooler) plugs, and NGK BR9ES if still cooler needed.
L-14U is a hot plug, according to information from the Denso, the manufacturer.
PMag Spark Plug Guide
I have been reading VAF and talking to folks who use NGK automotive spark plugs with their PMags. From what I have learnt I gather the following: First and foremost we should use plugs with a solid post terminal (tip), not the equivalent model number with the screw-off tip. There have been...
vansairforce.net
Let's clarify. When you say "GAMI injectors", are you speaking of a nozzle and restrictor combination, both sourced from GAMI? When you tried 0.024 "injectors", were you swapping both nozzle and restrictor, or trying the AFP 0.024 restrictors in GAMI nozzles?
Got it.
I've never examined a GAMI nozzle for Lycoming. Do they have four bleed holes, or just one?
Cool. The photo below nicely illustrates the purpose of the bleeds, and apparently more bleeds are better, based on reports like Rex posted above.
rexbrewer
Active Member
The DENSO cooler plugs made no difference, thinking now it's not pre-ignition. My IO-360, 9:1cr, GAMI spread 0.2gph, still gets rough at high fuel flow when leaning with WOT. At 6500' toc WOT lean to about 12gph when roughness starts (and EGTs spread instead of move together). If I reduce throtte/mp to 24" leans smoothly. Why not from WOT???
