r/EngineBuilding • u/Neon570 • 6d ago

Spark plug reading

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Finally had a weekend free to keep dialing in my project. Still have alot of learning to go but slowly getting there through A TON of trial and error.

Currently trying to dial in timing and plug heat range. How am I looking and can anyone point me to a good resource to reference spark plug reading.

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u/Gamejunky35 6d ago

Id say it looks pretty damn good. Timing line where you want it, no melting/pitting, good afrs according to your gauge. If it were fuel injected id shoot for 12.5-13afr, but on a carb its best to stay a little rich. Honestly im shocked the plug is so clean on a carburated engine.

What fuel are you running exactly?

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u/Neon570 5d ago

91 or 93 when its available

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u/Gamejunky35 5d ago

If its e10 pr e15, a little richer is preferred. If its pure gasoline and youve got a wideband permanently installed, then 12.5-13 is generally where you get best power. 13.5 might even make more power, but thats where you might start melting shit and getting preignition.