My new-to-me Turbo Aztec is now getting the TLC is has missed for several decades. On last run-up it showed considerable mag drop on both engines. I went ahead and flew it, leaning carefully to attempt to "burn off" the plugs, to no avail.
An off-the-chart EGT suggested a partially-plugged injector also. While in process of cleaning the left engine injectors, I decided to pull all plugs and see what was up. Clearly, several of the bottom plugs weren't firing at all. Looking in the plugs' high-voltage towers showed the typical screw that identifies the old-style Champion plugs, so I pulled out the trusty Fluke 87 VOM and checked the internal resistors. Results as per attached picture. (Yes, I know that is not the recommended way to check the resistor, but I think it's pretty revealing. (Acceptable values are .5k to 5k. The "M" is megohms - one million ohms.)) What few people know is that - aside from making the engine run - the plugs serve as snubbers to keep the mag voltages at reasonable levels. Firing an essentially open circuit (28 megohms, for example) can cause the internal mag coil voltages to rise high enough to flash across coil windings and ruin the mag coil.
When we were racing motorcycles in high school, Champion plugs were considered to be worthless. My opinion has not changed. I'm raiding the bank account for 24 Tempest fine-wires. It's ramen for me for a while. LOL.
An off-the-chart EGT suggested a partially-plugged injector also. While in process of cleaning the left engine injectors, I decided to pull all plugs and see what was up. Clearly, several of the bottom plugs weren't firing at all. Looking in the plugs' high-voltage towers showed the typical screw that identifies the old-style Champion plugs, so I pulled out the trusty Fluke 87 VOM and checked the internal resistors. Results as per attached picture. (Yes, I know that is not the recommended way to check the resistor, but I think it's pretty revealing. (Acceptable values are .5k to 5k. The "M" is megohms - one million ohms.)) What few people know is that - aside from making the engine run - the plugs serve as snubbers to keep the mag voltages at reasonable levels. Firing an essentially open circuit (28 megohms, for example) can cause the internal mag coil voltages to rise high enough to flash across coil windings and ruin the mag coil.
When we were racing motorcycles in high school, Champion plugs were considered to be worthless. My opinion has not changed. I'm raiding the bank account for 24 Tempest fine-wires. It's ramen for me for a while. LOL.
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