One particular of the benefits associated with being to able to focus on motorcycles is that you can generally find them pretty cheap when work on them is required. Typically, a bike that needs work has recently been sitting for a while, usually with the reservoir empty. This means over time that rust has taken over, as was your case with a 1981 Honda CB650 that I had acquired. To say that this thing had rust in it was an understatement; completely chunks of rust. Thankfully though, the tank experienced no pin hole escapes or anything and was completely solid. Now to the enjoyment part! I actually will describe the taking away rust from a motorbike gas tank. As We stated, this was done on a 81' CB650, so it's tailored to that, but I'm sure it'll focus on most other bikes.
What you have to pick:
Acetone
Distilled water (it's important that you only use distilled water)
Two heart stroke petrol
A length of chain four to 6 feet long
Rags
Some thing to plug the gas outlet (I used a tiny piece of hose a tiny rag and a part of black tape)
ESSENTIAL NOTE: ACETONE AND RUBBERIZED DO NOT MIX! If you are using rubber to seal the fuel output replace it whenever you drain the acetone mix as the acetone will eat away at it.
At this point I'm going to imagine you have the gas tank off of the motorcycle and that it's bare. Here is a step by step.
Plug the fuel output and make sure it is closed
Fill the tank about 1/2 packed with acetone and let it sit turning occasionally
Wait over night
Tremble the tank and clean the acetone/rust mixture into a bucket
Fill the tank 1/2 way again with acetone which time drop the chain in
Shake the tank often and vigorously. The string will knock remaining corrosion off
Empty the acetone/rust mixture into the box
Fill the tank plan distilled water and vacant it out. Do this until only fairly clean water comes out and no rust can be heard rattling around. I actually put a hairdryer in the fuel hole and dried it out right after
Fill the tank about 1/4 with two cva oil and shake it around then empty it
Please dispose of the acetone and other awful chemicals properly
I highly suggest installing an in-line fuel filter on the fuel line in between the tank and carburetor. It will filter out any small particles and keep them out of the fuel system. This product worked for me, my CB650 ran like a dream after cleaning the tank like this! The next phase is to give the carb a good cleaning.