How To – Troubleshooting Lawnmower Starting and Performance Problems

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    Small Engines found in Lawnmowers normally work well for many years. If you have a problem with your lawnmower starting or operating to the best of its ability it is normally a small adjustment that needs to be made rather then a replacement.

    One of the main ways that you can tell if your engine is still worth saving is if it smokes a lot of gray smoke through its exhaust. Gray smoke normally points to a problem with the piston rings where black smoke could mean a carburetor adjustment or spark plug needs to be replaced.

    It is often difficult to tell the difference between a simple smoking problem and one that means internal parts are damaged beyond repair but you should do your best to cure the problem before you start looking for a new lawnmower.

    Diagnosing Lawnmower Starting Problems

    Engine Is Hard to Start

    If the engine won’t start when it is cold then check the following:

    The air filter can become clogged. Normally air filters do not need to be replaced you can wash the foam filters in warm soap. Try starting the lawnmower with the filter removed. If it starts then clean or replace the filter if it is damaged.

    The gas cap vent hole could be clogged. Remove the gas cap and try starting your lawnmower. If it starts right up then clean the cap or replace it.

    The vent hole on top of the gas cap is plugged, creating a vacuum in the fuel tank. If the engine starts when you remove the gas cap, a plugged vent hole is the problem. Clean out the vent hole.


    The air filter is clogged. Remove the air filter unit and try starting the engine. If it starts, clean and replace the filter.

    Make sure your spark plug wire is not lose and inspect the spark plug for problems by removing it and giving it a visual inspection. If the plug is saturated with oil it means there are internal engine parts that are wearing. If the plug is cracked or has a worn electrode replace the plug.

    Choke Position is another easy problem to miss. Some engines on snow blowers have a manual choke and some lawnmowers have a start position on the throttle. Make sure you place the choke in the start position for starting then move to run or increase the idle once the lawnmower starts.

    Bad Gasoline is another problem that happens more in the beginning of the season. If you think you have water in your gasoline you can drain the fuel tank and refill it with new fuel. Some fuel bowels on the carburetor have a drain pin you can push to drain it. If you don’t  have this feature simply let the lawnmower sit until it cools and then pull the start cord until fresh gas enters the fuel system.

    Dirty Carburetors can also cause hard starting or dying on inclines. If your carburetor looks dirty use carburetor cleaner and then let the solvent evaporate for a few minutes before you try to start your engine.

    Some but only a few carburetors can be adjusted a carb that is out of adjustment or has a bad float level can cause starting and running problems.

    The engine won’t go to full speed. Check the throttle cable for binding. Sometimes when you remove the air cleaner you may find that it is binding on the throttle cable.

    The engine vibrates while running. This can happen because of a bent or out of balanced cutting blade. If you recently hit a rock or stump or other obstruction inspect and replace the blade if necessary.

    If the engine is lose on its mounting plate tighten it.

    Normally not a problem but sometimes the improper type of oil can cause problems for engine starting and performance. Make sure you are using the right type of engine oil and that you did not overfill.

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