My 8B suffering from pre-ignition

[Minimichael]

Ethanol free gas. Good octane. And I keep getting pinging or piston slap or whatever on my little Briggs 8b flathead (2-1/3hp?)...

Was thinking it could be the missing 2" blower plate extension I removed from the shroud top, at the head. (I know I said all this in older post, but I'm bored).

It also occurs to me now that the 3-legged coil on this one is a lil' chopped, in that I rebuilt it with a Tecumseh electrical assembly. (This required removal of the windings and shaving approx 3/16" of stacked plate material from along the sides of the armature's middle leg. (Anybody see Roadking805 do this on YouTube?) Just fit the new Tec electrode assembly onto the modded middle leg with some Bondo. Well, it worked, but I wonder now if that procedure changed the timing – which seems likely now that I'm thinking about it. Or would it not, cuz there's still the points?

As an aside, I removed a good amount of timing by shaving about 1/8 of a key width and not only did that hurt torque, but the pre-igniting persisted!

So, well, blah blah blah later, I had the flywheel off to install a stock key again and I just thought I'd post some closeups of my points..

 

[sparkwizard]

Piston slap on old air cooled engines is pretty loud. If you really muffle the exhaust, the mechanical knocking is insane. FWIW
You could install a degree wheel and hook up a cheap timing light to verify your suspicion.

 

[Minimichael]

Maybe it's not technically piston slap then. But pinging? It's more of a fast, high-pitched clank that happens when I'm accelerating hard from a stop. Also feels like a missed combustion event, and like a weakening of torque. You would notice it even without the sharp "clink", and for a split second makes ya think the rod may have cracked in half. But then it keeps goin

 

[sparkwizard]

Have you tried a colder plug? What brand plug are you running?

 

[Minimichael]

I messed with plugs, but don't recall what's in there now. I see timing lights at goodwill a lot..

Here's my action list, then:
1. Confirm timing
2. Colder plug
3. Reinstall top of shroud flap at head

...oh, and wait for spring!

 

[sparkwizard]

Be sure to check your thermostat, too.