About a month ago, while flying down low looking at a field out in in the country, had some sputtering and rough running. Yikes, changed to the right tank and started looking for a place to put it down. It smoothed out after 30 seconds or so, I flew home, no longer in the mood to look at fields.

OTG, sumped the tanks, found a small amount of water, put her in the hangar and thought that must have been the problem. Couple of weeks later, flew around the pattern a couple of times, no issues.

Today, flew over to 4M3 for some 100ll, filled her up, then climbed to 3500 AGL to practice an emergency descent. On spiralling down, no sputters, no issues at all. After doing a touch and go, climbed back up, did some steep turns first on right tank, then switched to left....a couple of minutes or so later, sputtering returned, this time really running rough, perhaps some popping (hard to tell for sure with the headset on). So I went into another emergency descent, this time with more urgency! Switched to the right tank, landed long but got stopped before running out of pavement. About the time I started taxiing, engine smoothed back out!

I borrowed chocks from a cropdusting service there, powered her up to 2000 rpm on both left and right tanks, she ran fine. With some trepidation, took off and climbed to 5000, still at the airport "just in case' and she ran fine so nervously pointed the nose for home, about 20 miles away. No issues, no sputtering.

Both times the sputtering happened it was on the left tank. Today there was no water in the tank although there has been a little on from time to time, I guess my fuel cap on that side may let some rainwater in--she does stay outside after flights for a day or two (to let the belly oil drip off into the grass!) and it rains fairly often here.

Any thoughts on this would be appreciated. Intermittent magneto issues? Water in the tank that is only going through the system when turning?

What say ye?

Thanks in advance,

Jay