Blower: Engine Misfires

If your leaf blower has a 4-cycle engine, a broken or weak valve spring could cause a misfire. The valve spring provides compression for the intake and exhaust valves. If the valve spring is broken or worn, the compression required to fire the engine will not be created, resulting in a misfire. Because of the pressure these springs are constantly under, they can wear and crack, and you will need to replace them before your leaf blower operates properly. The valve spring works closely with the intake and exhaust valves, so if the spring is not the problem, the valve could also be damaged or stuck.

A sticking or damaged intake or exhaust valve could cause a misfire in a 4-cycle engine. The intake valve allows air and fuel to flow into the cylinder, and the exhaust valve allows exhaust gasses to exit. This process is critical to the combustion process. If the valves are stuck, your engine could misfire. Sometimes the repair process is as simple as cleaning debris from around the valve, but if the valve itself is damaged, it will need to be replaced.

The flywheel is critical to the combustion process in your leaf blower. It controls the timing on a 2-cycle engine. A broken key can allow the flywheel to become offset on the crankshaft, causing the timing to be off, which results in a misfire. If you’ve already checked your spark plug and ignition coil and have determined that they are in working order, you may want to check your flywheel. In order to replace this part, you will have to open up the blower casing to access the flywheel for repair.

The spark plug in your leaf blower receives voltage from the ignition coil to create a spark. Simultaneously, the piston pressurizes the air and fuel mixture which is then ignited by the spark plug. This is the process that allows your blower to run. Over time, oil can accumulate on the spark plug and this can cause it to misfire. Oil buildups are very common on 2-stroke engines, and are often caused by an improper mix of oil and fuel. When your engine is misfiring, you should remove the spark plug, clean it off, gap it, and the re-install it. However, if you notice any deposits, corrosion, melting, or oxidization then the plug should be replaced. Additionally, if the engine spends most of its time revving high, installing a cooler running plug will allow it to dissipate heat more quickly, and this can help the issue. To confirm a plug is bad, you will need to test the ignition coil to ensure it is working properly. If the coil is working properly, the plug is most likely the issue. Spark plugs are inexpensive, so it is usually advised to simply install a new one and see if it fixes the misfire.

The spark plug boot covers the connection between the spark plug and the plug wire. If the boot is cracked or torn, the current can ground to the frame rather than going to the spark plug, resulting in a misfire. If your spark plug boot is damaged and you plan to replace it, you may find that adding a drop of liquid dish soap to the old boot will help you to pull it free of the old wire. Before you install the new spark plug boot, be sure that the terminal spring is still intact. As with any leaf blower repair, be sure that the engine has cooled down and the ignition switch is set to the “off” position before you begin.

The ignition coil in your leaf blower works with the flywheel and the spark plug to supply the charge that ignites during combustion. The ignition coil’s role is to supply voltage from the flywheel to the spark plug. Therefore, if you have a bad or damaged ignition coil, your engine could misfire. Before you check the ignition coil, make sure your spark plug is still in good working order. To test the ignition coil you will need a spark tester, which will accurately recreate the cylinder conditions. Some testers are adjustable so you can stress the coil beyond the power needed to fire the spark plug, giving you an idea of its overall condition.