Since the OP based his post on "sputtering" and can't seem to tell us whether it was rich or lean, all of this advice is likely not going to fix the problem. He also said "it didn't do that on previous flights" I will say it again: Side mounted side exhaust engines do NOT go rich on inside loops, EVER unless the tank is Ludicrously high. As for too much oil; there are hundreds of LA46's out there running on GMA 22% oil fuel that run perfect. We fly them every week-end and experience no issues what so ever. In addition, we don't run idle bar plugs and they run perfect, 4-4, 4-2, wet 2-2 depending on aircraft and propeller. Any plug with a heat range in the #3 zone works fine, or Thunderbolt Std. Typically a properly designed Schnuerle port engine doesn't require an idle bar. Of course, none of us run a clunk tank with questionable plumbing and we know how to adjust a needle valve.
When people post questions about things like "Quits inverted", "Sputters", "Won't Start", "has no line tension" the most helpful thing to do is ask for more information and explain that you can't diagnose the problem without it. The OP's problem could be as simple as the needle setting is too lean (or too rich but doubtful)