Rust at top of tank (inside)

[muzzy]

My CB750 has a very fine /dust rust inside the top of the tank, Its only where the fuel level has not reached.
I have removed the tank and sloshed fuel around I cant see any discoloration or sign of the rust coming off.
The rest of the tank is perfect only area is the very top of the tank that doesn't see fuel.
Any comments or suggestions much appreciated

 

[kirky]

i used white vinegar and salt

 

[WhiteWidow]

I agree with kirky, on the vinegar process but never heard of adding salt. A test was done on YouTube with different types of vinager. I can't recall which vinager was better, search YouTube for the answer... When putting your bike up for storage,
I found that draining the tank then spraying the inside with WD-40 prevents any formation of rust. WD indicates WaterDisplayment. Modern Fuels are POSION to a Metal Tank if left to sit for an extended period of time.