So I thought I would start a new thread to let folks know what I found. I am far from an expert but maybe folks can learn from my experience.
So after emptying the fuel, it was apparent that my 1978 moby 50V tank was pretty darn rusty. When I put my finger in the tank and felt around I could feel a significant crust and not just surface rust.
I did two vinegar treatments for 24 hours each, and flushed with DI water, but I was not satisfied with the results. So I picked up a gallon of Evaporust and treated the tank for about 30 hours (only at about 65 degrees though) and dumped the results into a large pan. I strained this for reusing. FYI: I recommend a cloth (old t shirt) strainer and not just a normal funnel strainer to get the smallest bits.
After emptying I looked in the tank and was really impressed with the results. But on emptying I flushed with a bit of DI water and could tell right away there was a blockage on the lower end. Thus I went out and did the garden hose flush and HOLY COW, the amount of stuff that came out was amazing.
So if I have only one piece of advise... if you have a really bad fixed tank then you need a considerable flush after the treatment. I ended up turning the bike over and flushing from the bottom. I had to do this on high for at least 5 minutes before things really ran clear. I just can't see doing that with DI water or anything else. You need pressure and volume. And compressed air did not do it, I tried. I had to use the water.
After it was done I used the air gun to dry the tank out, then I put the treatment back in. I am not sure if this is necessary but given the amount that came out I wanted to be safe. I will let it sit another 24 hours and then repeat the flush. If things look good I will dry with air and fog it with carb cleaner (I hope this is ok, if not please let me know).
For those folks who are not sure about Evaporust, I can tell you it does work. I can't imagine a tank so bad that it would not work. Get your gallon from Tractor Supply and not an auto parts store, you will save at least 25%.
Well finger crossed. When its over I am going to run an in-line filter just to be safe and see what else might come out.