“I have a little subcompact tractor. 1980 Mitsubishi that has mechanical injection and it would probably run on biodiesel with some modifications.”
They are all ready to go with any kind of veggie oil and as you know even deep frier oil, Most diesel sold today is “blend” Biodiesel. For others reading, as you also know Pollard the first diesel was designed to run on peanut oil. Just have to melt them back to a liquid first. The more recent applications of this concept are dual fuel. They run the exhaust through an additional tank with the alternative fuel.
Start it on diesel, and when the heat from the exhaust melted the fuel in the other tank they switched it over from diesel. I have a friend who builds diesel motorcycles and he runs straight up almond, corn, or other vegetable cooking oils with no problems at all.
That's what I've read about it. There is also a group of guys that when diesel was up over $4 during the obama years, came up with 85/15 used motor oil/gasoline. WMO(waste motor oil). It has to be filtered and having one of those high speed spinning machines that separate luquid by viscosity is good to have. Can't remember the name of it.