A bad fuel solenoid can present itself in many ways, and you’re probably familiar with them already. Symptoms may lead you to think the issue is related to other engine components like a bad fuel filter or clogged fuel lines. Knowing the right signs will save you time and direct you straight to the fuel solenoid.
I’ll share with you the right signals to look out for when using your riding mower and an easy test you can carry out to confirm if the solenoid is, in fact, the cause of the issue.
How to Spot a Bad Mower Fuel Solenoid (The Short Answer)
Trouble cold-starting, the engine suddenly shuts off, erratic idling, and hesitant acceleration are all tell-tale symptoms of a bad mower fuel solenoid in action. The solenoid’s sole function is to either stop or allow gas flow, and defective units fail to carry out this task.
Watch Out for These 4 Symptoms of a Bad Fuel Solenoid on Your Mower
Solenoids can work on-again-off-again or not at all, so even the same symptom can vary in how it reacts. Here is my list of 4 signs to look out for when diagnosing a bad mower fuel solenoid.
Trouble Cold-Starting
A faulty solenoid can cause issues with the engine’s starting, particularly noticeable when the engine is cold. The engine will struggle to get fuel to the combustion chamber, which can take some time. Try switching it off and back on again after the engine is running. If it is a problem to restart it, then the solenoid is likely at fault.
The Engine Suddenly Shuts Off
If the engine doesn’t receive fuel, it will shut down. If the engine abruptly stops for no apparent reason, it indicates that it’s starved of fuel. A defective solenoid can lose the energy needed to activate the electromagnetic solenoid and result in reverting to the off position causing the lack of fuel.
Unsteady Idling
If you’re like me, you like to allow the engine to warm up for a minute or two before you use it. During this idling stage, you may find the engine dies and then lets out a peculiar sound just to let you know it has a problem. Again this is because the solenoid becomes unenergized and switches off.
Hesitating to Accelerate
When the mower is under load by driving or engaging the blades, you will feel a distinct lack of power. Solenoids don’t just fail in the ON/OFF position – they can stick in a “halfway position”. If the solenoid decides to stick in the halfway position, you may find idling fine and slow RPMs ok. But once the engine is put under load at maximum RPMs, it will become starved and slow down, indicating a bad solenoid.
A Simple Test You Can Do to Diagnose a Bad Mower Solenoid
The easiest way to test a fuel solenoid is to remove it and run power through it. You’ll find that most solenoids will activate using a 9v battery even though they are 12v. Double-check this if you can or just head straight for the 12v battery.
Solenoid works much like light bulbs, and it doesn’t matter which way you connect them; they will still work. Polarity (+/-) can be made in either direction, so you’ll probably not find a +/- on the solenoid.
First, take the solenoid and work the mechanism by pushing and pulling the center pin. Check for friction. If you feel resistance, it may just be gummed up and just needs a clean.
Then connect the solenoid to the battery and observe the action. When you energize the solenoid it should move into the housing and when you disconnect the power it should come back out. If at any point this isn’t done smoothly, even after it has been cleaned, then it’s bad and means that the solenoid needs to be replaced.
I wrote a whole post on how to test a lawn mower solenoid, so if you want to learn more be sure to check that out.
Riding mower won’t start after sitting overnight. I have to blow in gas tank and it fires right up.
Hi Keith,
It sounds like you have a problem with the fuel pressure/flow. Riding mowers usually have an OHV (over-head valve) that creates pressure/flow for the fuel pump to work. When you’re blowing into the tank, you are doing the job of the OHV. So, if you look on the side of the fuel pump, you should see three pipes:
Fuel pipe from the fuel tank
Fuel pipe going to the carburetor
Air pipe coming from the engine to the fuel pump
You want to make sure that there is air coming out of the pipe from the engine into the fuel pump. Also, there should be a 4th small pipe going from the carburetor directly to the fuel tank. This pipe also regulates the pressure. You need to check it and make sure it’s still attached and isn’t blocked. Finally, take a look at the fuel filler cap. There should be a tiny hole to allow pressure out of the tank and stop a vacuum from forming. Make sure this isn’t blocked. If it is, you should be able to clear it with a pin.
I hope this helps you get up and running again.
Cheers, Tom.
Same thing happened to me…fuel line was bad, permeated,causing line and pump to loose their prime. Replaced fuel line and fixed the issue 🙂
Hello Tom
We have a 14.5 hp Briggs and Stratton engine on a riding mower. When I first start it it will run ok at full throttle under load, but after 3 or 4 minutes it acts like it is not getting enough gas and i turn mower off and I still have to use choke to nurse it back to our shop. Now i am wondering if it might be the carburetor solenoid not working properly?
Thank you for any advice you could give me.
Harold Marten
Hey Harold,
Well, it seems that cold starting is ok, but when it warms up, there is a problem. So, I would try to run the engine for a minute or two at idle, then a minute or two on half power, then again for a minute or two on full power. I’d do each of these tests with the mower stationary and with the blades off.
I would want to figure out if it’s a lack of fuel or an overheating problem. Either of these can be a problem with the carburetor. If you are using the clutch, you’re playing with the air-to-fuel mixture, and, again, this is the carburetor.
If the mower is ok at lower speeds, then it could be a lack of fuel. This would make me look at the fuel lines and fuel filters.
If the mower is getting hot at lower speeds, then I’d be thinking about vapor locks and boiling fuel. The carb’s mixture settings could be off, hence why the choke helps. Solenoids can cause this issue, but they tend to do it randomly and not under specific conditions.
I hope this gives you a few ideas 🙂
Let us know how you get on.
Tom
23.4 Kohler V-twin – after engine heats up, power is greatly reduced or shuts off. Engine sputters and I have to “limp” it back to barn. The fuel solenoid is directly above the muffler (bad design in my opinion) and I’m thinking it is damaged. Thoughts?
Hi Charlie,
First, I would check that your lawn mower can cool itself by checking the oil level, the oil filter, and the cooling fins on top of the flywheel.
Next, I would remove the fuel solenoid and energize it off of your mower’s battery and quickly see if it’s working or not. If it struggles to engage, then you’ll definitely need a replacement.
It sounds like you could have an issue with your lawn mower being starved of fuel when it needs it. So, I would want to work out if the lawn mower has an issue with low revs and high revs. If your lawn mower is ok on low rev (needs less fuel) but bad on high revs (needs more fuel). If the problems start when the mower is running on high revs, then I would take a look at the whole fuel system. Here’s what I would check:
Check the flow through the fuel lines, through the fuel filter, from the tank, and through the pump, and check the line from the OHV to the fuel pump.
Finally, if everything appears to be ok, I would then pull out the carburetor jet to make sure it’s not clogged.
I hope this gives you a few ideas.
Tom.
T1600 Craftsman riding mower. Briggs & Stratton engine shuts off after about 30 minutes of use, cools down and then starts again.
Hi Dave,
If your lawn mower works when it’s cool and stops when it gets hot, then I would say that it is an overheating problem. So I would suggest that you take a look at the following items:
1) Dirty air filter: A dirty or clogged air filter can restrict the flow of air to the engine, which can cause it to overheat.
2) Low oil level: The oil in a lawn mower helps lubricate the engine and keep it cool. If the oil level is low or the oil is dirty, the engine can overheat.
3) Dirty or damaged cooling fins: The cooling fins on the engine are designed to help reduce heat. If they are dirty or damaged, they won’t be able to do their job effectively, which can cause the engine to overheat.
I’m pretty sure that as long as your lawn mower isn’t being overworked, then one of the potential issues I listed is the cause.
I hope this helps, and thanks for the question.
Tom.