+1 Took a friends 140 for a spin yrs ago to exercise it, not realizing in my youth that a sump drain located mid tank won’t be the low point when a tail dragger is on the ground (my t-craft didn’t have that issue). Ran perfectly sweet till leveling out at 800’, then my very young son asked why the plane was so quiet... After paying an unscheduled visit to the farm of my in-laws on one of their fallow fields, the water was removed by raising tail, then flew it back. Water trapped in the wrong spot is “undesirable”. Drain water, then add some fuel additive, and done. If that’s the issue here.