do the compression pull the gas into the cylinder on some lawnmower?

if gas is not going into the cylinder but gas is going into the float bowl but not going into the cylinder for the lawnmower to start, explain how this work.

3 Answers

  • Tony
    Lv 7
    7 years ago
    Best Answer

    Here's a little clarification: On a FOUR cycle engine, the first cycle (or stroke) is the intake stroke. The intake valve opens as the piston goes down creating a vacuum. Air rushes in and the carburetor mixes gasoline into that air stream. The second cycle (or stroke) is the Compression stroke. The intake valve has closed and the piston begins its journey toward the cylinder head. It compresses the gas/air mixture. Just before the piston gets to top dead center the spark plug ignites the fuel. As the piston crosses top dead center the fuel becomes fully ignited and begins to push the piston down (the third stroke - called Combustion). When the piston reaches the bottom the exhaust valve opens and as the piston begins to rise back toward the top the exhaust gasses are blown out of the motor. That's the fourth and final stroke of the engine. So it's not compression that pulls gas into the cylinder it's vacuum.

    However, on a TWO cycle engine, the crank case is bathed in a fuel/oil mixture. The same processes are going on as in a four cycle engine but they happen in a different way, resulting in a combustion cycle every two strokes.

    Here's how it works. As the piston goes down it raises pressure in the crank case. When the piston gets down so far ports open that allow the pressurized fuel to squirt into the cylinder. The piston begins to rise, closing off the ports and begins the compression cycle. At the top of the compression cycle the spark plug ignites and causes combustion. The piston is pushed down by the expanding gasses. When the piston gets down so far exhaust ports open up and allow the rest of the expanding gasses to escape, all the while the crank case has been pressurized again by the downward motion of the piston. After the exhaust gasses have been expelled (rather quickly) the intake ports open and begins the two cycles all over again.

    So it's (starting from a cold cylinder), the piston goes down and pressurizes the fuel air mix in the crank case. As it reaches the bottom that fuel air is squirted into the cylinder. First stroke is when the piston goes up and compresses the fuel/air mixture. The second stroke is after that compressed fuel/air mixture has been detonated and the piston begins down. Near the bottom of that stroke the exhaust port opens and allows the expanding gasses out. Further down the intake port opens and allows pressurized fuel/air to squirt into the cylinder. Thus, just two strokes to accomplish the same four operations - intake, compression, combustion, exhaust.

    Type in your search box "How does a two cycle engine work?" then follow some of the links. You'll probably find a better explanation along with an animated drawing that shows how it all works. You can do the same with "How does a four cycle engine work?"

    With regards your not getting fuel into the cylinder, it's probably a clogged jet. Carburetor cleaner will clean it nicely. Be careful if you're going to push wires through the jets, doing so can alter their size and affect how the engine runs.

    To test out whether the engine will run, dribble a little gasoline into the carburetor. Use a very small amount, then give the machine a pull. If it starts but dies quickly then you have good spark. The issue lies with just not getting any or enough fuel into the engine.

    Hope this helps.

    'av'a g'day mate.


  • 7 years ago

    Compression blows, vacuum sucks. If you have gas in the float bowl and the mower won't start it's bound to be a clogged main jet in the bottom of the venturi emulsion tube. Make sure you have spark. If you have 10% ethanol gas formula you will need to remove the main jet and run a wire through the hole. A torch tip cleaner works great. Sprays won't get the gummie ethanol out.

    Source(s): Mitsubishi Master Tech
  • butor
    Lv 4
    3 years ago

    Remove tank and pour out the contents or siphon the contents out utilizing a small hand pump (like the form used for bleeding brakes). Most of the time carried by means of auto parts shops. Fill up with gas. Gasoline is a solvent and will support dilute the oil. That's what i would do as it is simpler.

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