Hey guys, I'm kinda new to motorcycles so forgive me if it seems like I'm mentioning a lot of stuff you probably already know. But I have a 1980 flh and I wound up having some issues with it. It was cutting out on me as I was going down the road a couple weeks ago, wouldn't react to how I was working the throttle, just kept doing it's own thing revving up, lurching forward and then idling back down a few times until it finally came to a stop and died on me, this happened a few times in a day. So what I ultimately found the problem to be, or atleaat what I think it was, was rust on the inside of the gas tanks, it had actually plugged up the crossover line from the right to left tank. I got new lines and was working on removing the rust from the insides of the tanks. I read somewhere that you can use nuts and bolts and vinegar to remove the rust. I went and did this a few nights ago and left the vinegar in the tanks to try and soak in and get rid of as much stuff as I could but I just took a look and it didn't seem like it did much, maybe added some more rust I don't know. But my question is can you leave vinegar in the tanks for too long? I'm just afraid that I may have unintentionally added more to the problem instead of actually fixing it. Any help would be appreciated, thanks guys!

 

The old guys used white vinegar overnight.

 

You can try sulfamic acid (available as granular masonry etcher at Home Depot) mixed with water overnight, very effective at removing rust, and a little faster than vinegar. OR, pull out the heavy artillery and use straight muriatic (hydrochloric) acid, also available at HD, swish for just a minute or two, then flush with water-repeat as needed 'till rust is gone. DON'T leave muriatic in the tank for any more than a few minutes at a time.

In terms of time soaking to remove rust (from slowest to fastest):

vinegar (acetic acid) < sulfamic acid < muriatic (hydrochloric acid)

 

White Vinegar overnight, figure 12 hours. Dump and all the rust should come out. Do it again if needed. I then rinse twice with water then one last rinse with clean gasoline. Works like a charm.

Other acids can be very aggressive and you can get in trouble, the vinegar works pretty slow and is not going to kill you. Good luck.

 

There's a commercial product that's reasonably priced - Fertan (dunno if it's in the USA)

Tannic acid that converts iron oxide to iron tannate - the iron tannate is black and is pretty much as tough as the original iron was. It can be painted over and resists further rusting nearby (iron tannate cannot rust).

The down side is that is is black and needs to be painted over. But it works.

 

hey guys, if I'm using vinegar do I need to remove the tank internals?

 

Vinegar is weak acetic acid let it soak at least 12 hours and then do it again.
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https://www.evapo-rust.com/

 

there are products like wonder, ospho and such that will remove the rust. however, i find these products will fail over time if used as a converter. they use phosphoric acid and other binders to convert the rust to ferrous phosphate which is inert like the other poster's product. however, over time, the converted rust will separate from the base metal and leave a pit that will now rust again. these are great products when used in the open and can be applied when needed, used an ocean of them in the offshore environment. that said, it will never be as good as a blast and paint. so for the tank, you can use them as a dissolver, but do not let it dry, flush with water.
in times passed, i used to roll the tank with steel shot till i was satisfied and then coat the insides, another story there, all liners are not equal.