You jump on your riding mower, fire it up and flip the lever to engage the blades and…NOTHING. The engine stalls. And it does that over and over again. That’s obviously no good and can get old pretty quickly. But you’ll be glad to know that if your riding mower stalls when the blade is engaged there is often a simple explanation. I’m going to talk you through a few of the most common causes of this problem and how you can fix it.
Riding Mower Stalls When Blade is Engaged: Common Causes
There are a few things that I’d recommend you check if your riding mower stalls when the blade is engaged, some more involved than others.
Something Stuck in the Blade
This might seem like a painfully obvious reason for your riding mower to stall, but it’s easy to overlook given you actually can’t see what’s going on in the deck unless you get off your mower and lift up the hood.
If you’ve got something particularly large in there, like a large stick or part of a branch, your blade isn’t going to go anywhere. And if the blade isn’t able to move, the mower’s motor will come under more and more strain, trying its best to break the blade free, but when it can’t, it’ll stall.
This video highlights this issue perfectly:
Solution: All you need to do to fix this is to carefully remove the obstruction. Make sure your mower is definitely shut off and the blades are not set to “engaged” before you do anything. You might need to use a small jack to lift one side of your mower up to make the obstruction easier to get at.
Safety Switch Under Seat Faulty/Not Properly Connected
There are a few different safety switches on most riding mowers. They’re designed to protect you against accidental injury, but when they’re not working properly, they can cause problems.
There’s one such safety switch located under the seat. It detects when you’re actually sat on the seat, and deems that it’s safe to engage the blades. But when you step off your riding mower, this switch detects that and won’t let you engage the blades. The reason being, if you’re off the mower and the blades are engaged, you could potentially be fiddling around with the deck and hurt yourself.
However, if this switch is faulty or the connection is loose, it may stall when you try to engage the blades even if you’re sitting on the seat. It’s simply not detecting that you are.
Here’s a good video to illustrate this:
Solution: You can access this sensor by lifting up the seat on most riding mower models. The first thing would be to pull it out of the connection and then blow on it. It could be dust or dirt causing the problem. Plug it back in and see if that fixes the issue. If it doesn’t, you might need to replace this switch.
Bent/Damaged Spindle Pulleys
Your riding mower relies on a series of spindle pulleys and a drive belt to turn the blades. If you’ve ever had problems with either of these parts – a mower deck belt that keeps coming off, for example – you’ll know both how vital they are and what a pain in the ass they can be when something goes wrong.
If any of the spindle pulleys are bent out of shape or are not spinning properly, the belt won’t be fed around the deck properly, and this could cause the engine to stall. If your belt has been coming off frequently or worse yet, your lawn mower belt keeps breaking, this is a pretty clear indicator that something is wrong, and the pulleys need to be checked out.
Solution: Shut your riding mower off completely and raise the deck or disconnect it and remove it. You need to be able to get at the pulleys to test them. You’ll also need to remove your mower belt for this. Sometimes damage will be obvious at a glance. But you should work your way around the deck and test each of the pulleys to make sure that they’re spinning correctly. If you find that any of them are damaged, they may need replacing.
Exposed Wiring
If any of the electrical wiring that’s used on your riding mower has had the insulation worn off and this comes into contact with metal, it will ground out the engine and cause it to stall. As you’re having issues with the mower stalling when the blade is engaged, it might be worth checking any wiring that this lever could come into contact with.
Solution: This will require you to play the role of detective and may take a bit longer than some of the other fixes that you’ll find on this list. As I just mentioned, I would start by looking for any wiring that could come into contact with the blade engagement lever. If you do find any exposed wiring, cover it up with some electrical tape.
You Need a New Battery
If a riding mower stalls when the blade is engaged, one of the most overlooked things is to check on the condition of the battery. Lots of people get fixated on the fault being mechanical, but as you can tell from this list, it can often be electrical.
If you’ve had the battery for a good length of time and it’s shown signs of struggling in the recent past (maybe issues with slow starting), it may be causing the engine to stall when you engage the blades.
Here Rob Douthit explains this issue very well:
Solution: The solution here is very simple; you need to buy a new battery. It’s also worth asking a pro what the recommended battery is for the specific riding mower model that you have. It could be that your current battery was already underpowered (fewer cold cranking amps) and that has further compounded the issue.
Thank you for providing such a comprehensive overview of the issue. My John Deere e150 riding mower works fine until I engage the mower deck 🙂 When I do, the engine cuts off. Over and over again. I’ve recharged the battery, changed the fuel line filter, made sure that the fuel flow to the carb is steady, and I drained some stale fuel completely and replaced it with fresh fuel (87 Octane). I looked at the safety switch under the seat. When the engine is running and I get off the seat, the engine cuts off; so, the seat safety switch seems to be OK. I did not know to look for frayed wiring along the wire harness but will do so per your advice. Unfortunately, I did see that the mower deck is completely crooked, which I can tell by comparing the position of the deck wheels in terms of proximity to the rider’s back wheels. One set of deck wheels is about 3″ closer to the back wheel than the other side of the mower deck, so I know the deck is twisted (probably from slamming into a root or whatever mowing where I cleared out a lot of brush).
I am completely frustrated as I have two acres of lawn to cut. I’ll follow your instructions and see where I end up. If all else fails, I’m buying a goat. Thanks again. PS- How do you do with advice about a 1960 Farmall Cub that I restored but cannot keep running. Talk about a frustrating venture.
Hi Thomas,
Sounds like your lawn mower is totally fine when the blades are not engaged, so it’s not an issue with the engine. So, the crooked deck is probably what is stalling out your mower. What I would do is remove the deck belt and then try engaging the blades. If the deck is the problem, then disconnecting the belt should stop the issue. Now if you disconnect the deck belt and the problem persists, then I would check that the clutch is working. How does the mower sound when it’s stalling? Does the mower shake like it’s trying to engage the blades? I had this situation before where the mower would shake, and I would hear squealing from one of the belts, followed by the engine stalling.
What I would do is remove the belt, remove the deck, and see if the problem disappears. If it does, then you’ll know where the problem lies.
As for the 1960 Farmall Cub, this is a little bit beyond my experience.
Good Luck.
Tom.