It took a while to burn up what low-octane, ethanol-containing fuel was still in the system, but once it did, the tractor’s engine suddenly ran smoother, and the sputters all but all but disappeared. So now I know that either the ethanol or the low octane in the other gas is what was causing the trouble. I just don’t know which.
Premium runs for well over $3 a gallon around here, which isn’t great, but still better than $4 a gallon. If the octane is the determining factor, less expensive, slightly-higher-octane premium gas would be better. It took running a lot of the regular through this tractor to make the trouble appear, so if I were to experiment I’d need more than a gallon, but preferably less than a full can.
The manual might tell me ethanol is the culprit, but I’ve read that about all lawn-mower engines — and this is the only one — walk-behind or riding — that’s ever had trouble with the grade of fuel I put in it.
The deleterious effects of ethanol, as I understand them, are cumulative over long periods of time: seals and such deteriorate. I would not want to extrapolate from automotive experience, since almost all modern-day cars and/or trucks are able to fiddle with ignition timing to compensate for octane rating, something I suspect is not true of lawn tractors. But this sentence may give it away: “It took running a lot of the regular through this tractor to make the trouble appear.” Which implies an almost-empty fuel can, which in turn implies some sort of heavier-than-gas gunk that sank to the bottom of the can.
An experiment suggests itself: get some 87-octane E-zero, if it’s anywhere nearby to be had. (Locally, it’s about $2.90 a gallon, 35 cents or so higher than 87 E-10.) Interestingly, 91-octane E-10 runs about $3.10, but I’ve been paying $3.219 for 91-octane E-zero, and using 5 percent less of it.