How to Troubleshoot a Honda 50cc Moped


Mopeds are a great way to commute around town, through your suburb, or up large hills. Although 50cc moped engines are known for their reliability, every once in a while they will break down and quit running. Luckily, a 50cc engine has one piston and one carburetor, making everything very easy to work on. There are three reasons that mopeds will stop running: a dirty carburetor, a bad spark plug or misaligned ignition points. If you can fix these things, your moped will be up and running once again.

Things You'll Need

  • Screwdriver
  • Wrenches
  • Gloves
  • Spark plug (If stock spark plug is worn-out)
  • Carburetor cleaner
  • Starter fluid
  • 5-gallon bucket
  • Air compressor

Starting Your Moped Back Up

  • Check your spark plug on the moped. It is located on the front of the engine. Unscrew the plug. Now, try to run the engine with the spark plug protruding out of the engine. If you can visibly see spark, it works. However, if you cannot see spark, check the model number on the side of the spark plug and purchase a new spark plug with the same number.

  • Spray starter fluid into the carburetor's air filter, and try to run the moped. If the moped runs for about 5 seconds and then dies out, the problem lies in the carburetor. This can mean a number of things, such as your carb is dirty, or the jets inside the carburetor are plugged up. Either way, you will be able to fix these with a little bit of work.

  • Clean up your carburetor by taking it apart, and soaking it overnight in a 5-gallon bucket of carburetor cleaner. Carburetor cleaner comes in an aerosol can, so just try to empty the can into the bucket, and let the carburetor soak in it.

  • Take the carburetor out of the mix, and let it air-dry throughout the day. Don't try to towel-dry. You may end up plugging up some gas jets with little bits of paper towel.

  • Force air through all of the little holes in the carburetor using an air compressor. Make sure to get every hole that the gas may go through, as any little rock or piece of dirt can stop the flow of gas, shutting down the engine. Once you have forced air throughout the carburetor, put it back together.

  • Place the carburetor back onto the moped. It should run like new again. If you are having trouble with speeds, read Section 2.

Troubleshooting a Working Moped

  • Look at your carburetor, located on top of your moped's engine. Protruding from one side, you will see a screw that has a spring on its threads. Using a screwdriver, turn that screw all the way in, and then screw it out one-and-a-half turns.

  • If your top speed is slower than 30 miles per hour, do an overall cleaning of your moped. By this, I mean that you should do the following:

    Clean the carburetor
    Wipe down the outside of the engine
    Oil the piston head
    Check the tire pressure
    Remove rust from the fenders, handlebars, etc. using steel wool

    Doing the above can and will increase your top speed, just because your moped will now be in factory-like condition.

  • If you are looking for a higher top speed, consider purchasing a big-bore kit, which includes a larger carburetor, bigger piston head and new gasket set. These kits sell for around $200, but you will see at least an eight-mile-per-hour increase in speed. You can get these speed kits online at,, or

Tips & Warnings

  • Wear gloves at all times when working on your moped. This helps prevent grease that dries skin from getting on your hands.

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  • Photo Credit spark plug image by Yali Shi from moteur de moto image by Emmanuel MARZIN from
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