Hey don't knock it that looks like my float I pulled today also out of my 78. the rest of the tank looks the same.
People say that they put chains inside the tank and swish it around to knock off the crud. I don't see how with the Reserve and main line screens in there.. I was able to clean the screen thru the gauge hole with a carb cleaner spray can.. Honda wanted $575 for a new one. If you can still get one somewhere.. why can't they make them out of plastic for replacement.. I really don't know how to clean the barnacles but have to try.. I thought about a handfull of 3/8 nuts and Swish them around.. Just keep away from the screens.. I tried a liquid rust cleaner but it don't really act like rust.. I cleaned off the Gauge and it was still shiney underneath the crud.. I opened the Gauge and was able to clean it enough where it worked with my Ohm meter.. I am open for other Ideas also about the crud.. I may try a wire brush I have a 12" extension and can run that on my Drill.. I see why there was a added filter under the seat.. I saw one on ebay but who can say it don't look like ours.. My tank had 2 gallon of stale gas in it when I got the bike.. the gas didn't cut the crud.. I accept all advice on what to do next..
These guys http://www.cyclepsycho.com/ used to sell clean but not coated tanks very reasonably. Like just over a hundred $ IIRC.
I have heard great sucess stories using electrolisis. It is not as difficult to setup as a lot of folks think. You might try doing a search on it.
I took mine to a Radiator shop and had it done by a professional. He used Red Kote and according to the shop owner the tank will now outlast me. Cost was 150. Talking to others that may be a bit high.
I will use phosphoric Acid I hear that works good and won't harm the tank. I really don't see Rust, mostly the Crud and barnacles. So will try that first.. If the 78 tank is coated I don't want to damage that. They say Pour 15 flakes off sometimes and makes a bigger mess. once you get it clean if you store it full of gas with stabil it will not rust anyway...but, I cannot guarentee that..
Just an update on my gas tank for future reference. I had to go with acetone and Muriatic Acid not leaving either one in too long and flushing in between treatments. I had some 20 year old dried up gas on the bottom to dissolve. I tried fuel injector cleaner to get it off the screens in the bottom of the tank which did not work. Finally I used Carb Cleaner and that dissolved it. Also I used baking soda to neutralize
The coating just fell off it was so bad, but the metal was solid with no pitting.
I bought a coating kit from eastwood.com that I'm going to use to finish the job.