I know other areas of the forum have beaten this topic to death, but not in regards to the effect of modern fuels on older machines. I'm just curious about what others are feeding their old machines and if anyone has noticed more power or lower rates of consumption on certain fuels. If anyone has a comparison of the effect of modern fuels on the combustion chamber, I would also be interested to hear that as well. I have never opened up a two-cylinder after running it on modern fuel.
My M was run on 74 octane at its Nebraska test, but I've never seen 74 or 'tractor gas' for sale before because I guess I'm not old enough. The manual for my G (it was an all-fuel) said that it could run on basically anything that could burn once it had warmed up. Due to the price of kerosene, I only ever ran it on gasoline.
I have run just about all modern grades of gas in my '50 M, '52 G, and my little Sears with an I/C Briggs & Stratton; regular 87 octane, 87 e5, 87 e10, premium 92/94 octane, 92/94 e5, and even some low-lead 100 octane av-gas. I have never tried e85. I have noticed a few trends and was wondering what other people's experiance has been compared to mine.
Generally speaking, a higher octane seems to yield slightly better fuel economy in situations where the tractor is working harder, but in light load situations it does not seem to make any difference. My G would very consistently burn about 1/2 a gallon less per hour while plowing with a tank of premium. Pulling a hay wagon or the firewood wagon had no effect.
Also generally speaking, all of my old machines seem to run smoother with ethanol-free fuel. This could be that the only ethanol-free gas I can get is higher octane. I have tried e-10 regular fuel with and without a few different kinds of "ethanol stabilizers" in an attempt to isolate the ethanol as a variable with varying degrees of success. Without knowing what the different additives are and how they effect the fuel's hydrocarbon molecules or combustion it is hard to really know what is a band-aid covering up the effects of ethanol, or what is actually neutralizing it. I have not found anything I would consider to be conclusive. Furthermore, the cost of adding $12 of additives to each 10 gallon tank of fuel drastically increases my operating costs and makes ethanol-free premium a cheaper option.
A friend had some gas left over from his race car that he didn't want sitting around in his garage for a year, so he gave it to me to burn up. Plowing at night with 100 octane av-gas was fun because I had fire coming out of the stack when the govenor opened up! Probably not good for the exhaust valves so I turned the carb down. I don't think the lead in the fuel really did anything one way or the other for the G.
Obviously modern fuels are "fine" to run through old tractors. I'm probably over thinking this a bit more than it needs to be, but I like it when things are better than just "fine".