Who knows what may have been put into the tank before you got it? No 2-cycle mix I know of would cause such deposits.

Rust and varnish will raise h#!! with a steel tank. Especially if it sits for several yrs. I have had a couple of cars with bad tanks and it aint pretty. I have also junked other wise decent BS lawnmower engines simply because the tanks junk would clog the carb.

"I bought a moped that had been sitting for many years and the fuel had dried up in the one-gallon tank in the frame. I was able to fill it and get it running but over the years, the gas would quickly turn brown and particles would cause problems in the carb jet."

How old is this machine - 30 years? It sounds like you bought a Moped that had sat for many years and that you have had an ongoing problem for many years since then.

The sludge is the result of oil and gasoline being left to evaporate many times. I would clean all of the fuel system out completely. Then be sure to keep the tank filled with fuel and use it regularly.

"I decided to fill the tank with NAPA carb soaking cleaner and with the use of air bubbles, sand, soaking time, removed all the deposits, which amounted to about 2 cups worth."

Two cups of sludgy deposits?? Wow!!

You are describing a typical problem of metal fuel tanks. Moisture condenses inside and causes rust. To prevent this in the future you can keep the tank completely full during storage, use a fuel stabilizer, or apply a liquid tank coating inside the tank (many Harley dealers stock this coating as this was a common problem to older motorcycles.)

I bought the moped in 2003 and started really having problems last year. The tank came out pretty clean using air bubbling and coarse sand.

Here is a picture of the dried deposits. For the amount of deposits I had, and they were along the entire length of the two foot long frame tank, the gas must have dried out many times. It's a 1978 Guzzi Robin.

The lumps in the picture are about 3/8" in length.

{{gwi:132088}}

Wow. I didn't take into account moisture in the tank. What a mess.

How would I apply the tank coating? I can't spray it in there.

The tank sealer is poured into the tank, sloshed around, then the excess poured out. Some folks call it "sloshing sealer".

Wow! Looks like it might have been stored in a dirt field with the gas cap off!

No, it was garage stored. It was in showroom condition and 25 years old when I bought it at the man's yard sale for $35. It had 400 miles on it. He and his daughter had a newspaper route in town and they bought it brand new in 1978.

Anyhow, I put gas in it today and took it for a test ride. I guess it's trustworthy enough to take to work now.

By the way, he called me last year and asked me if I wanted to buy its twin, which he also bought new in 1978. Only this time, he wanted more for it because he had installed turn signals. The new price was $40.