When premium is not so, ah, premium
When a dealer mechanic in the 1970s, a Wing came in with an odd engine noise on rapid decel. I confirmed this as a very loud and increasingly sharp tapping when the throttle was yanked open then allowed to snap shut. Interesting. The customer insisted on disassembly, and the findings were very heavily carboned exhaust valves and faint witness marks on the pistons. Yup. There was so much carbon that on decel the valve's closing was slowed slightly and the piston actually kissed the valves, making the noise. The customer admitted to using premium gas. Fast forward almost 40 years, I'm training manager at Kawasaki corporate, and a dealer needed help with a bike because of an unsolvable high speed misfire. Upon disassembling the engine, we found something interesting, and it took me back to that aforementioned Gold Wing so many years before: heavily carboned exhaust valves. What was happening was the same as with the Wing. The valves were hanging open slightly at full rev. But in this case the bike's computer, sensing a cylinder compression change and programmed to protect the bike's catalytic converters, intermittently disabled the ignition system to do so, resulting in the misfire. Wow. Bet you didn't know vehicle ECUs were that fancy, eh? Here's the point. Using detergent and solvent laden premium fuel, really designed for crusty old cast iron V8s, is a bad idea for the relatively modern, highly combustion efficient Japanese motorcycle engine. In all but a very few exceptions, 87 octane unleaded is what the Japanese design their engines for.
Grandma on speed
I want to put what I said about K&N air filters into better perspective. When a mechanics instructor I used to have certain sayings with which I reinforced my instruction. One was "pressure differences, pressure differences, pressure differences!" This particular mantra -- and it became just that to my students -- reminded them of the underlying principle behind carburetion, and also electricity (more specifically, voltage), and a surprising number of other things covered in that six week long, five hour a day freshman-level introduction to the main technical disciplines within powersports mechanics. One of my favorite of these sayings though was, "...like putting your grandmother on speed." (What?!) I used to say this on several occasions, for example when we explored why it is bad practice to introduce to a battery a richer electrolyte solution than recommended. Because, I warned, though it might perk up a worn out battery, it would be like putting your grandmother on speed. The battery's useful life is fast-forwarded into a shorter period. There's a trade-off of performance at the cost of durability. It got their attention. And it's true. And it's true of K&N air filters as well. Your bike's engine has built into it X number of hours or miles that it will perform as designed while fed properly filtered air. But giving it bigger gulps by also allowing more contaminants in is simply using up that designed-in, normal lifespan in a bigger hurry. Like giving your grandmother amphetamines. This is my bone to pick with the K&N. It seems wasteful to me to trash any engine, but especially a historical, significant machine by deliberately accelerating its timeline in the name of "free performance". But here's the deal. If it's worth it to you -- and who am I to tell you what to do with your 40-year old motorcycle -- then great. More power to you. I just think you should know all the facts. Poor old grandma.