Hello! When it comes time to lay up a moped for the long winter’s nap, I’ve found a technique that will keep the fuel tank and carburetor very clean and help get things off to a smooth start in the spring. This will be particularly helpful if your bike has an in-frame fuel tank, a design not known for easy accessibility and cleaning.
You’ll need a couple of fold-top sandwich bags and some sturdy rubber bands. Round up a medicine dropper and a measuring cup and that completes the equipment list.
When you’re returning from the final ride of the season, turn the fuel petcock off a short distance from home so whatever fuel is downstream from the petcock will be consumed and not left behind to gum things up. There’ll probably be a very small quantity of gasoline lurking in the carburetor bowl, but we’ll deal with that momentarily.
Once you’re done riding, remove the gas tank cap. Disconnect the fuel line at the petcock, connect a short length of fuel hose and route it into a gas can, then open the petcock and drain any remaining fuel. Make sure to also switch the petcock from On to Reserve to empty as much fuel as possible.
Next, take the measuring cup and mix approximately one cup of gas line antifreeze with Sta-Bil and Marvel Mystery Oil. Some owners may prefer other brands. The choice is yours.
Now, take the medicine dropper, extract a very small dose of the ingredients you’ve mixed together and shoot it into the carburetor’s fuel line fitting. This will keep the bowl clean and prevent freezing over the winter.
OK, turn the petcock to Off, then pour the remainder of your potion into the gas tank. Install the cap, then take one of the plastic bags, wrap it closely around the cap and secure it with a rubber band. In a few minutes you’ll notice the bag has expanded somewhat. This is a good sign. It means the tank is air tight and your potion is fermenting, so to speak. And, after a short while, you’ll see the bag contract and shrink around the gas cap. This is another very good sign. The tank is under a vacuum and no air is entering.
On my bike (a Tomos Sprint A55) I like to seal off the air box intake port where it enters the opening in the frame. A small piece of plastic wrap and a rubber band work nicely here. If you like you might use the sandwich bag and rubber band to cover the air intake at the carburetor. It all depends on convenience and accessibility.
While we’re at it, I also use the plastic bag/rubber band approach to cover the end of the muffler/tailpipe. This prevents bugs and critters from taking up residence in the exhaust system.
When spring arrives I remove the rubber bands and plastic bags. I drain the potion from the moped's tank and dump it into the car's tank. (A little upper cylinder lube won't hurt any.) I then mix a gallon of ethanol free gasoline with semi-synthetic 2-stroke oil, and into the moped's tank it goes.
I used these tricks over the first winter I owned the moped, and I’m pleased to report that she started on two kicks at the beginning of the new riding season. Not bad at all. Hope these tips work well for you, too.