You might say this is as viewed from 6000 feet...
...where I live...
Since the rebuild (in 2013), I have noticed an annoying trait that developed on the bike, which is: it would sputter on hot days in city traffic (95+ degrees F, no wind, lots of stoplights, etc.). When I would pull away from the stop, it would 'snap' as the clutch closed and sometimes even 'pop' back thru the carbs (notably #2 and #3). And, it would get mechanically noisy, and hot enough to not be able to touch the oil cap.
Hmm...this is not normal for my bike.
Then, 3 weeks ago, it started happening to my car, too (contagious?). in heavy, hot traffic, it started acting similarly. I thought something went wrong, like a jumped timing gear (it only has 320k miles on it, what the heck...), as I had to re-tune the timing and carb to get the car to idle at all when hot in traffic. After changing the timing gear and finding it was only 25% worn to the "limit" (i.e., that's not the problem's source), I was really scratching my head.
After one more event like this with the bike, I realized: the carbs are boiling in the bowls, MUCH worse than this used to be (when ethanol first appeared). It used to happen with the Vetter lowers on the bike in hot, heavy traffic, so I ride in the city without those. Switching from my usual next-door gas station (Shell) to Phillips changed nothing (makes sense, they are both owned by Shell), switching to Conoco gas got me to 100 degree days before it happened again.
Wednesday this week I stumbled across a station with ethanol-free fuel, and immediately filled up: it completely solved this problem in both vehicles. The carbs don't boil now, even in 100-degree weather (Wednesday was that hot, today only 95-ish). The bike has returned to its long-appreciated (by me) personality completely, and it was all due to the gas.
The EPA is pushing to make 15% ethanol in our fuels, instead of the 10% seen in most places now. If you have not already, consider contacting the AMA to participate in their conversations with the EPA to stop this nonsense, as this will quickly damage your engine's valve stems and top ring(s). All 3 grades of fuel here in Colorado are now as clear as water, indicating that any form of lubricity is now gone entirely from the fuels. The "bronze" colors we used to see in gas was from various compounds that were intended to help lubricate top ends and keep things clean: now they instead have cleansers similar to astringents, which strip any lube from the top end altogether. Be sure to add an ounce or two of some sort of oil to your tank, at least once in a while, to give the valves and rings a 'break'.
