Thanks! Though the rest of the bike has a lot of rust, the gas tank is particularly clean. I suspect the PO used premix instead of the oiler system.
Good Job JVB! I think it did better than the vinegar - and the three days! I was going to use some acid, but I've been trying to stay away from the serious etchers. And I didn't have any in the house, so, like you, I used what I had!
Just because I had it on hand, I used straight Simple Green and a handful of 1" washers. I shook the tank a few dozen times and let it sit overnight. I was pretty surprised it came out so clean.
By the way, how do you test the oiler system? I want to make sure it works, or I will use premix.