How to Tune Up a Two Cycle Engine




Introduction: How to Tune Up a Two Cycle Engine

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All two-cycle engine tune-ups involve the same parts: spark plugs, air filters, and fuel filters. This article explains the basics of a two-cycle engine tune-up.

Small engines are used in all kinds of power tools and lawn & garden equipment, and like all engines, 2-cycle engines should get a tune-up at least once a year.

The most common mistake that small engine owners make about tune-ups is waiting for the engine to stop working before doing one.

Tune-ups are intended to keep an engine running, not to fix it once it stops. If your engine has stopped working, its possible that the problem could have been prevented with regular tune-ups.

This article explains the steps for a simple 2-cycle engine tune up, including air filter, spark plug, and fuel filter replacement. We use a Shindaiwa T242 Trimmer as a demonstration model for this tune-up, but these steps apply to all 2-cycle engines. 

You will need the following items for this tune-up:

  • a ratcheting socket wrench
  • a new air filter
  • a new spark plug
  • a new fuel filter
  • a hooked wire

Step 1: Replace the Air Filter

Air filter housings are located in different places on different engines, but they're usually in an accessible area on the outside of the block. In the case of this Shindaiwa trimmer, the air filter housing is located on the side of the engine.

Your engine's air filter will be visibly dirty when it's ready for a replacement, and like other tune-up maintenance items, it should be replaced at least annually.

To replace the filter, simply remove the air filter housing, take the old air filter out, install the new filter, and then close the housing.

Most air filter housings open and close with a simple screw.

Step 2: Replace the Spark Plug

The engine's spark plug should be replaced next. To replace the spark plug:
  • First remove the spark plug boot.
  • Use a ratchet to unscrew the old spark plug.
  • * Install the new spark plug with the same ratchet.
  • * Replace the spark plug boot.
Replacing a spark plug only costs a few dollars and takes only seconds to do, but the difference in performance will show in your tool's engine right away and throughout its life.

Step 3: Replace the Fuel Filter

Replacing a 2-cycle engine fuel filter is the most complicated part of the tune-up, but it is still very easy to do.

The fuel filter is connected to the end of the engine's fuel line which rests at the bottom of the fuel tank. To replace the fuel filter, you will have to fish the fuel line and filter out of the fuel tank.

This where that hooked wire comes in:

  • Using the hooked wire, fish the fuel line and fuel filter out of the engine's fuel tank.
  • Pull the old fuel filter off of the fuel line.
  • Install the new fuel filter by pressing its end into the fuel line.
  • Drop the fuel line and filter back into the fuel tank and make sure that it rests at the bottom-center of the tank.

The end of the fuel filter that attaches to the fuel line is barbed. After it is pressed into the end of the fuel line, the barbs help it to stay attached.

The filter needs to rest at the bottom-center of the tank so that fuel can still get to the line when the trimmer is tilted or turned on its side.

Step 4: Conclusion

There are a few more things that tool owners can do to tune-up their small engines, but replacing filters and spark plugs are the most important.

Start your 2-cycle engine tune up by entering your tool's model number at the top of this or any website page. The "Search By Model Number" field will take you directly to your tool's parts page where you can get the filters and spark plugs you need.

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    2 Discussions

    Bruce Lefebure
    Bruce Lefebure

    5 years ago

    Just bought a rebuilt boat motor, the lift tube in the gas tank was kinked and didn't know it. After first start the primer bulb on the gas line wouldn't ciphon, I tapped on the gas valve on motor and it helped, but still seems like the engine is running rough. What should I do?


    5 years ago on Step 3

    When my Weed Whacker wouldn't start I started checking different things. I changed the plug. It'd start briefly if I primed it, but I realized something else was wrong. I found the fuel line broken in pieces. There are 2 lines coming out of the tank. The top one goes to the priming bubble & the other's below that & goes into the engine. Which one is the fuel filter supposed to go on? How do I replace the line(s)?