That coughing and sputtering is leanness. I certainly dealt with it on Brad and I's mini Carolina's spine raid. I'd tuned the Mighty Scura in 40 F temps with no alcohol fuel, and it was fine. Hadn't ridden it since. On the trip, the first time I put gasahol in it, it sneezed a couple of times going back out on the highway. It *never* does that. Farther into the trip as it got hotter, it showed a lot of just what you guys are talking about. Didn't like running at low speed at all.
What was the difference? CO trim. I had dropped it 20 points when it was cold and straight gas, and it was fine. Once on the trip, and I was getting 50 mpg (!) I thought, "Uh oh. Sure hope it's not TOO lean." Nothing I could do about it without GuzziDiag. I lived with it for a week, and the first thing I did when I got home is bump the CO trip back up 20 points. Runs perfectly again.