Some Strombergs(aka Tractor Carburetors) have mixture controls and some don't. The Stromberg on my 85 Champ has a mixture control wired to full rich. The 65 that was on it before didn't have one. I had no problem with fouled plugs with either engine.
Strombergs - My reccollection is that the small engine carbs in Champs and Cubs do not have a mixture control. So you cannot lean when taxiing making the distance to the runway the largest factor in the build up of lead in the plugs when running 100LL fuel. Another reason to find a grass airport where you do not have to wait for takeoff behind a bunch of IFR departures.
"I haven't had any plug fouling problems yet. Don't know if its the leaning, the Marvel Mystery Oil, or the sacred Paul Poberezy talisman on the altar in my hangar." I vote for the statue of "Pope" Paul.
Best of luck,
Wes
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