RE: Cleaning up old engines
I have used a mixture of alcohol and oil to soak the engines in that for a few days. You can also use some old fuel that you are not to sure of. After that, I tear them down, clean and oil them, then put them back together. Sometimes, when you have engines with bearings the are too corroded they will need to have the bearings replaced.
Now I have heard of guys boiling the engines in antifreeze (after they are apart to clean them) I have never bothered it is amazing what some oil and alcohol will remove.
Good luck
Just to be sure, as far as fuel, I am talking about glow fuel....