[HWYSTR455]

AVGAS, that makes sense, I would bet the yellow is from the additive in the AVGAS.

I'm not a fan of running AVGAS, the additives were not made for ground level gas engines, and do more harm than good.

You might not be getting det, but you will be more prone to pre-ignition if the plug is too hot. I would consider a 2 step colder plug and go from there.

Yes, the XR5 3332 is an appropriate choice, as is anything that crosses from an AC R43S, like a Champion RJ18YC. If you're still in a testing phase, you can run the standard Autolite plugs like the Autolite 83.

I get pretty frustrated at time with NGK nomenclature, a lot of their' stuff translates to 'in between' heat ranges, like they go 1.5-2 steps in either direction, so they really don't cross right. When I ran iron heads, I always used either the AC R43S or the 44.


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