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Hi guys and welcome back to my small engine repair channel. Today, I'm going to show you how to fix a lawn mower that surges up and down. By surging up and down, I mean when you hear the engine rev up and then rev down non-stop, creating a very annoying noise.
I will take the mower outside and start it up so you can hear what I mean. You'll notice that it's surging up and down, which is very annoying. This is caused by a lack of fuel to the engine, specifically a carburetor issue.
To fix this problem, the first thing you want to do is turn the fuel valve off. Then, you need to take off the air filter cover. Using a 10 millimeter socket with an impact, undo both bolts while paying attention to the order of all the parts. Disconnect the fuel line and the linkage, keeping in mind that there will be some fuel left in the carburetor.
Clean the dirt off the carburetor by blowing it with air and using some carb cleaner. Remove the bowl using a 10 millimeter socket or wrench. The carb doesn't look too bad, but usually the carbs are dirtier when they surge up and down like this. Also, remove the needle valve and the float.
The main issue causing the surging is the small jet inside the carb. Sometimes, the small jet under a screw can also cause the problem. To remove the small jet, use a slotted screwdriver and tap the carb if needed.
Now, remove the emulsion tube. To stop the surging, enlarge the jet hole a little bit. Make sure to clean all the tiny holes on the side of the emulsion tube and ensure that the center hole is clean all the way through. Use a torch tip cleaner to run inside the jet and blow some air to clean it.
Once the inside of the carburetor is cleaned and the emulsion tube is inserted correctly, tighten everything up. Reinstall the float and the needle valve, making sure they are clean. Insert the needle valve in the hole and put the pin back on. Reinstall the bowl and the 10 millimeter bolt.
Now, clean the part of the carburetor that goes to the intake. Make sure everything is cleaned and run the tip cleaner in any holes that are present. Remove a screw to access a small jet under it. Use a micro drill bit to expand the hole in the jet but be careful not to go too big. Tap the carb upside down to remove any shards.
This is the process for a Honda engine carburetor. The process may vary for other carburetors, so I have another carburetor to show you how to access the jet on that one as well.
In conclusion, fixing a lawn mower that surges up and down can be fixed by cleaning the carburetor and expanding the small jet hole.
