Both old and new lawn mowers have some rev up and down issues. It’s not like you have the updated mower, and you don’t face unstable rev issues frequently. It means your engine is facing mostly airflow issues that slow down your engine and can’t flow the natural air. That’s the ultimate answer to why does my lawn mower rev up and down.
I face a similar problem for different reasons. I found the top ten reasons that play a crucial role in creating rev issues. If you face a similar situation, I’d suggest going through these problems and sorting them out eventually.
1. Insufficient Airflow
Insufficient airflow is the very first reason why your lawn mower rev is unstable. You cannot expect the regular running speed from your lawn mower if it has a poor or damaged airflow system. Sometimes, the air combustion may go wrong and create a problem eventually.
It will then create an unstable rev problem and hinder the engine running speed. You should check the entire air system of your mower and clean it accordingly. It will solve the rev up & down problem accordingly.
2. Contaminated Fuel
Apart from insufficient airflow, the contaminated fuel may cause unstable rev problems. Mainly, the contaminated fuel will go through the entire fuel system. In the meantime, the lousy fuel will create problems in the engine. When you start the mower, it will not get the quality fuel to run it smoothly.
Moreover, the contaminated fuel may come with additional particles that will create a clog in your engine fuel system. Eventually, your engine will start to run slowly and go up and down frequently. If you face such an issue, you must check your fuel quality. You may need to change the fuel and pour some quality engine oil if needed.
3. Lack of Fuel
Another common problem is lack of fuel. If your lawn mower engine doesn’t get enough fuel to run, it will stall. That would be another reason why your lawn mower is facing rev problems or unstable engine performance. You cannot expect to run your mower smoothly without having enough fuel.
Your engine may struggle to start or go down after running for a short distance. It’s entirely based on your oil quality & enough oil in the oil tank. So, check your oil level and sort out the rev problems within a while.
4. Damaged Spark Plug
A spark plug is another crucial part of your engine. You must regularly clean the spark plug and repair it if it gets torn or displaced. If your spark plug is damaged and detached from the main switch, the engine may be unstable. That will be another reason why your lawn mower faces rev up-down problems frequently.
When your spark plugs are damaged poorly, you must replace them. Otherwise, the revving problem will be there permanently. It may damage your mower engine slowly and create other issues.
5. Faulty Carburetor
When you start the mower engine, it needs an air and fuel mixture ignition. Here, the carburetor plays the main role in creating the ignition and starting the engine instantly. If it doesn’t work correctly or gets damaged, the faulty carburetor will hinder the engine’s performance. It may cause rev problems and eventually damage the engine performance.
If your carburetor stops working and doesn’t create the ignition, check its health and replace or repair it accordingly. You cannot expect to avoid rev up-down problems having a faulty carburetor.
6. Clogged Airfilter
Sometimes, the clogged air filter may create a rev problem and unstable the engine performance. Using an old air filter may get too much dust and other contaminated ingredients from the surroundings. Eventually, it will stop working and make the engine unstable.
You may be able to run the engine, but it won’t run smoothly. If you use the clogged air filter, it will damage the mower engine permanently. So, clean the air filter and solve the unstable engine problem.
7. Vacuum Leaks
If you buy the updated lawn mower, you must have the vacuum. If you use it for years, you might have vacuum leaks. These leaks might create unstable revs for the lawn mower. You should either replace the vacuum or repair it to cover those leakages.
You cannot even think of using a leaks vacuum since it can damage the engine indirectly and lower the performance. This is why the lawn mower engine remains unstable.
8. Fuel System
Fuel quality & lack of fuel are not the only reason behind your rev instability. If the fuel system or fuel tank goes wrong or gets damaged, it will directly hamper the engine performance. If the damage is too hard or destroys the entire fuel system, you cannot even turn on your engine. It’s the worst scenario of unstable rev conditions.
9. Gas Tank Issues
Another reason is gas tank or fuel tank problems. Sometimes, the fuel tank might get some dirt or debris from the contaminated fuel. In that case, the gas tank will fail to provide enough fuel to your mower engine. Therefore, you must clean your gas tank regularly to avoid such an unstable rev problem.
Often, the gas tank creates so many problems that you cannot but replace it with a new one. It’s a lengthy process and might cost a decent budget. You can save your rev up-down by cleaning your gas tank regularly.
10. Other Problems
There might be other problems regarding the engine cooling system and heated air combustion system. If they get too much dust and become clogged, they will create an unstable rev problem for your lawn mower. You cannot skip them to get a better solution.
You can only identify the damaged part and try to repair it. If you still find the rev instability, you must replace the damaged cooling system or heating elements. It will help you to maintain the sound health of your lawn mower.
When you ask why does my lawn mower rev up-down, you will get these ten reasons behind it. From my experience, they all are the most culprit in influencing the lawn mower to reduce the engine power and capacity. You may also add other reasons if you regularly use your lawn mower.