rusty gas tank trouble

my moped runs but when i found it, it was in a shed for 15 years with gas in it. i repaired it so it runs now but is there a way for me to get the rust out of the tank? without buying a new tank?

Re: rusty gas tank trouble

Use the search feature and type in rusted tank and you'll find all kinds of help and advise. good luck!

Re: rusty gas tank trouble

Ron Brown /


Here is a previous post of mine.


These instructions were originally written for someone with a "Tank in frame" moped so if you have a removable tank, some operations are a lot easier.

There have been posts on the forum refering to the use of gravel, BBs, nuts and bolts and other abrasive odds and ends which can be shaken up in the tank.

The only kit I am aware of for doing this is a Kreem kit, it is quite expensive but very good. It is difficult to use on a tank in frame ped.

I have used muriatic and phosphoric acid. I prefer phosphoric because it does not promote rust. Brand name cleaners have been mentioned on the forum which contain phosphoric acis such as CLR and Naval Jelly.

I would stick with the acid only approach, as opposed to buying a Kreem kit which coats the tank. If your tank is excessively rusted, to the point where gas is seeping through the rusty spots, go to a motorcycle shop, buy a Kreem kit and follow the directions. The coating will seal small holes.

Pick up a gallon of Phosphoric acid and a bottle of "dry gas".

Most buisinesses using large stainless steel vessels use Phosphoric acid. Dairy farmers, dairy products, brewerys etc. Posibly you could call one, or just stop by, it is cheap and they may just give you some. I have also heard that it is sold in Meijers pool section so I suppose other pool supply stores would have it. "Dry gas" is available at auto parts and gas stations for removing water from your fuel system.

Whem you use it, you are going to have to figure out how to get it back out of the tank safely. Typically, with a removable tank, you can just duct tape over the holes and dump it by removing the tape. You must remove the petcock and removing the gas cap is a good idea as it has a vent hole which can leak acid.

If the petcock scews into a threaded hole in the tank, maybe you can find a brass nipple that will fit the thread and allow you to drain the acid safely. If you have no choice but tape, remember that a running hose is your best defense against disaster.

For all of the following, keep a garden hose available and turned on. Wear old clothes, there is a good chance they will become religious, as in holey. Work outside, away from anything which could get splashed. When rinsing, use a lot of low pressure water, high pressure will send acid to places where it may do damage before you find it.

Dilute some acid in a plastic container and test it with a piece of rusty steel. You want it to remove the rust in about ten minutes but you are not looking for a violent reaction.

Remove the petcock and plug the hole with something appropriate, good duct tape usually works. Remove the gas cap if possible, if not, cover the hole with saran wrap before closing the cap to keep the vents from filling with acid.

Pour enough diluted acid in the tank to almost fill it. Seal the filler with tape or the cap/saran wrap and slosh the acid so that it is cleaning the top side of the tank. Just rocking the bike will do this. Keep an eye open for leaks and rinse off any acid you see immediately with a slow hose. Keep sloshing every minute or so until your time is up as determined by the test above, then slosh and wait five minutes more.

I am not sure how you are going to drain the tank but if you have not figured out a drain tube, lean the ped so most of the acid will fall straight to the ground and keep a sready flow of water on the hose to rinse any parts of the ped which get splashed.

Btw, letting the acid run into the ground in your yard is not an ecological disaster. Many plants prefer acidic soil. Don't let your pets get near it, dilute it a lot and don't dump it all in one place, especially not at the base of a tree.

Check the inside of the tank to make sure you do not need another application.

Using a rinse and slosh tecnique, get rid of all the acid in the gas tank then dry off the ped. If you have an air line, blow out the tank. If not, dry it as well as you can with rags, paper towels, hair dryer etc. Then replace the petcock and pour a bottle of "dry gas" into the tank and close the lid. Slosh this around for a few minutes to mix with any remaining water trapped in the tank seams, then drain it out.

Add gas and ped away.

Re: rusty gas tank trouble

Dan Webber Kastner /

We should make this an FAQ.


my experience

I just cleaned rust from my tank recently, here's how I did it.

actual time spent 'sloshing' would depend on how heavy your rust is

I just do it !!!!!

Hi , me to , i have a old FLANDRIA 1974 and the tank was rusted. I strip all the frame and i bring it to a place where they repare radiator.

He cleaned with ACID and after he put a stuff (stiky sealer) insinde the tank. Now garanty for 10 years !!!!!

It cost me 50$ !!!!!!

Re: rusty gas tank trouble

I got all the loose rust out of my tank with muriatic acid , but it is still rusty. I have been using an in-line filter. Do you think this is safe? The rust in the tamk is not too bad, and the in line filter gets most of it out.

Re: rusty gas tank trouble

Matt Wilson /

Toehead.... your carb will most likely clog again. Think about how small a main jet is... it really only takes one particle to clog it up.

I cleaned a puch and a peugot with straight muriatic acid. I let it sit for 1 hour, drained it, sprayed WD40 immediatly after, and flushed with water for about 2 hours. You'd be amazed how much rush and stuff is in there.

Remove your petcock and replace it with a brass pipe fitting with a pinched fuel line. This way your tank will not leak, and the acid wont eat through your it did on my peugot.

You can get the brass fitting from the hardware store, for about $1. Bring your petcock to match the threads.


Re: I just do it !!!!!

Glad you got it figured out Alain... thats the right way to do it...

I hope it works good for you.

Re: I just do it !!!!!

Yes now, finish the rust in the gas tank.... ;)

With FLANDRIA moped, i need to find the idle speed with the gas cable !?!? No adjustment on the carburator...

Stange car ???

Re: I just do it !!!!!

It must be... but I have never even seen a Flandria... so I am not much help... there is usually one screw that either holds the slide open (on the side)... or holds the butterfly open (on the top).

Re: I just do it !!!!!

Ron Brown /


Idle #3.

Don't ask me what carb this was, maybe a Delorto round slide on a Moto Guzzi, but it had a rod with an end like a nail that fitted into a keyhole slot in the slide and the other end was threaded and anchored to the carb top.

Zippy also keeps talking about setting the idle by adjusting the cable slack, I think on Vespas. I'm not sure what that is all about.


I just adjusted my idle

Yeah Ron... Oh my god... I have worked on bikes with those!... I would say 60's Jap bikes had them... maybe some Brit bikes too.

Man.. those memories are sooooo old.

I am picturing these real antiquared looking carbs... little knurled brass knobs on top for adjusting the idle ... (not as bad as remote float bowls though).

Ped stuff is so 'old tech' generally... he could even have something like that.

Re: I just adjusted my idle

Ron Brown /


I just looked in the book. 1968 Moto Guzzi V7, Delorto round slides.


Re: rusty gas tank trouble

I bought a tank reliner kit called Kreem for $25 comes with rust remover, prep, and liner. Worked good, no problems

Re: rusty gas tank trouble

I got the local radiator shop to line my gas tank with a product like kreem for $25. Ask at a local antique car or tractor show who does it locally. I've been told that a gas tank can only be lined once and that it either takes or it doesn't so that's why I had it done by someone with more experience then me on the subject.


Re: rusty gas tank trouble

I also used the Kreme kit on my '77 Cimatti. Followed the directions to the letter and it worked perfectly. One warning, though: Be careful not to plug up the vent in your fuel cap with the stuff. It took me weeks to figure out that I had. The bike would start up, run great for a few minutes and then die. It wouldn't start again until it sat for a couple of minutes, and then the same thing would happen again. It turned out to be fuel starvation from a no-longer-vented fuel tank. I solved the problem by drilling a small hole in the top of the cap.

Also, once you've gone through the Kreme routine, make sure to clean your fuel filter and carb, and change your fuel line for good measure. They're probably all filled up with rust.

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