Lawnmower won’t start when hot, what to do

Approx Reading Time: 11 minutes

On a nice day you take your trustworthy lawn mower outside with the intention to trim your lawn. But somehow your Lawnmower is not running smoothly. You discover that it starts and runs fine when cold. However, starting it again when it is hot is an awful experience.

So the question is why is the mower difficult to start when hot? The main culprit is presumably a failing coil, but there can be other reasons as well. In this article, we will look at the various reasons and how to resolve the situation.

Lawnmower won’t start when hot:

  • A Defective Spark Plug not igniting the fuel
  • High/Low oil level
  • Flawed fins foundation of Overheated Engine
  • Loose nuts and bolts become the basis for leakage of air, causing insufficient air supply to the combustion.
  • A restricted Carburetor due to a faulty auto choke causing engine flooding
  • Problematic Compression due to inoperative valve
  • Presence of alcohol in oil.
  • Faulty ignition coil.

If you are unsure how to troubleshoot the problem, we have broken down the steps in simple and user-friendly instructions.

Common troubleshooting steps when your lawnmower does not start when it is hot:

We have identified seven reasons why your Lawn Mower will not, or is difficult to start when it is hot.

1. Defective Spark Plug

One of the most common causes of lawnmower engine not cranking is due to a faulty spark plug. There is a minimal gap between the two electrodes of the spark plug. It ignites across that gap and aids the proper air -gasoline mixture to combust and produce power. If this gap does not fulfill the optimum length requirement, the combusted heat widens the gap enough to shut down the mower. The spark plug’s spacing should be fixed according to the details given in your Lawnmower’s manufacturing manual. Moreover, the electrode can also weaken due to wear and tear.

Secondly, the buildup soot can also affect spark creation, and this incomplete ignition gives a hard time for the engine to start when hot. The hot start failures are mostly due to the wrong plug fitting. As we already know that the lengths and heat ranges are specified for spark plugs. Initially, you must inspect the correct plug code with your engine maker. It is an excellent practice to have a spare spark plug with you as it permits you to fix your problem swiftly by restoring the plug with a good one. After examining the sparking plug, if you find its components are not smooth, you will see that the issue is resolved, and your time is saved just by restoring the plug.

You can also not repair a defective spark plug; it is recommended to replace your spark plug at the start of every season.

2. Faulty plug wire

Plug wires are copper coils looped around a metal core. They work as the high voltage passes through them, searching for ground; positive voltage bounces from the plug electrode to the ground. The spark plug provides a perfect path to ground the voltage and spark ignites. This process took a couple of milliseconds. If we provide a relatively shorter path to the ground for the coil voltage, it will eventually shut down the mower engine because the voltage is not reaching the plug.

Therefore, when we emancipate the bail lever, the coil voltage achieves an ideal track to ground, the engine shuts off suddenly. And everyone wants a short cut whether it is human or machine. The engine will not run intermittently if any abrasion is faced by coil control wire against the ground source.

When the engine starts, massive combustion occurs; high-temperature values cause’ high resistance to the voltage flow, which is why plug wires generally breakdown when the mower is hot and begins operating again when the engine cools down. A precautionary measure always keeps your lawn mowers in ventilated areas because the greatest enemy of plug wire and electrical components is moisture.

3. Malfunctioned Carburetor

Your engine requires fuel or is getting too much air in a failing carburetor, which is the biggest obstacle in its smooth running? We’ll try to figure it out here.

– Does the engine gets enough fuel

Let us check whether the engine is lacking fuel or not. Lawnmowers may be fitted with different choke types (auto choke, manual choke, or a priming bulb) to start a cold engine and smoothly enrich the fuel mixture. Usually, the auto choke carburetors are prone to supplying extra fuel to the cylinder when starting hot; this phenomenon floods the spark plug with fuel that leads to a no start.  The gummed-up and sticky choke located inside the Carburetor is another cause for the hindrance in the starting engine, as it fails to provide the proper fuel ratio. Because it malfunctions, the engine stops working.

– Does the engine gets enough air

Another origin is the lack of ample air or provision of extra air for the flooded engine. The auxiliary air could be from a vacuum leak somewhere in the engine or a carburetor fault, whereas the air’s absence might be due to clogged air filters. For the appropriate AFR, remove the air filter and clean the air filters and chokes; otherwise, the air-fuel ratio is off. Gas engines perform their best when the air-fuel ratio is 14.7 to 1 that mean 14.7 parts of air to 1 part of fuel.

Most lawn mowers will typically have a lever to sway choke; advanced engines now offer a thermostatically controlled automatic choke system. So if you have an engine (auto-choke) with a hot start problem, go ahead and change the Carburetor. It is good to check the choke linkages, thermostat if exits, and clean the choke and air filters. If any of the elements has gone wrong, then the engine will stop. So, it is better to replace the faulty components if cleaning is not successful.

4. Low oil level

Engine components like coils and plugs will stall when they are above the optimum temperature limit, and the low rise in engine temperature is observed when the oil level is low.  Also, an initial start or push cannot be generated if the engine has a critically low oil level to protect the engine because it serves as a basis of coolant and lubricant in the engine. So, whenever you fill the gasoline, make sure you have checked the oil level.

5. Overheated Engine

Another frequent cause of motor engines not starting when hot is the overheated engine. The lawnmower engine may look small, but it generates a tremendous amount of heat when in operation. To dissipate such extreme heat, it has cooling fins. The sole purpose of the fins is to scatter the inoperable heat. However, when you mow the lawn, the grass clippings and other debris may clog or block the fins. These fins jammed with old grass stuff and debris for an extended period behaves like an insulation blanket, in return overheating the mower.

It will eventually stop running, and you will have to wait until the engine cools. The shroud or plastic housing can also trap enough dirt, debris, twigs, and clogs that will eventually lead to the engine shut off. Therefore, cleaning the fins and plastic covers once it is cool prevents the engine from stalling. What you have to do is take away the outer casing of plastic and eradicate the twigs and old grass with compressed air; otherwise, they become the prime source of holding heat close to the engine. When the engine cools, fire it up again, but it perhaps will bog down and stop once more after it overheats.

6. Air leaks

Loose bolts are commonly the source in a mower engine for shutting down when hot. Let me explain how. Loose bolts are a source of air leaks that force an engine to sucks in too much outside air, which abandon the appropriate gas-to-air ratio. When the engine gradually heats up, the remote units expand, and all gaps become larger. Ultimately, you came across the hard running of the engine that will sooner or later shut off.

Therefore, periodically you have to tighten the bolts that keep the motor frame and engine components together to avoid this problem; otherwise, these bolts will probably lose after their overtime use and make the engine of your mower shut off. Check and tighten the bolts, especially those that are linked with the air intake to the engine block. An important tip to check at times the bolts that secure the whole lawnmower frame.

7. Problematic Compression 

The compression issue is prevalent for mowers. It is mostly due to faulty valves. There is an easy way to figure out whether your mower is suffering from low Compression or not. If the mower’s starter rope seems to move easier than it used to be, it indicates the Compression is inadequate along with too large valve clearances, which is the foundation for another problem aggravated by a hot engine. If you do not know about mechanical components, you need to call a professional small engine repair person.

You can refer to a video as attached in this URL that explains the entire process:

Additional causes when your lawn mower does not start when it is hot:

Apart from the earlier mentioned reasons there are two additional reasons that can lead to your mower not, pr difficult starting when it is hot.

● Presence of Alcohol in oil.

Sometimes, alcohol in oil may be responsible for shut off. Many manufacturers recommend regular gas or e10 ethanol. As E15 and e85, when set on fire, dissipate much heat so, it will damage the engine because of the low boiling point. And it voids your warranty. You can solve the problem by merely placing a riser or non-metallic shim between the engine and the carb.

● Troublesome ignition coil

If your Lawnmower is new, though it is rare but possible, the ignition coil may have gone wrong. But if the mower is 10+ years old, the chance is high. The ignition coil and condenser control the flow of electricity to the spark plug. They must be in the best state, and if they are not, they should be replaced on a priority basis; otherwise, it can cause severe problems in starting the engine.

Frequently Asked Questions:

1. Starter does not crank when hot, what to do?

This issue is the case of heat soaked. It is merely a matter of absorbing and retaining heat from under-hood sources, for instance, from the exhaust. This heat adds up the resistance in the starter’s electrical component, which dramatically reduces the current flow. The limited current in the starter results in improper cranking. Diagnose the battery, cables, and starter before the operation.

2. Why Honda lawnmower won’t start?

First of all, inspect the spark plug to see if it is damaged by using a spark plug tester. When the engine is cranking, if there is a vital spark, then the spark plug terminals are not defective and vice versa. Replace the spark plug if it’s defective.

 A clogged carburetor can restrict the engine from starting, so replace it if it’s not working after cleaning. Insufficient or old fuel (gasoline) may be one reason for carburetor clogging; some components may evaporate with time leaving behind a stickier fluid that causes clogging. Old fuel also causes clogging of the fuel filter. You should check the ignition coil with an ignition coil tester for this issue, replace it if defective.

3. Torro lawnmower is not starting; what to do?

You should do a thorough cleaning of the mower if your Torro lawnmower is not starting. Do clean your mower’s Carburetor, and at the bottom of the float valve, there is a bolt; pull it out. Clean the tiny holes in that jet and make it sure by passing a wire through the holes. Also, clean the very tiny hole at the brass bolt’s top, which often gets clogged.

Final Remarks:

Indeed, a malfunctioning mower can be a significant source of distress. Being impatient in this case will not help you at all. Follow the systematical approach to solve the problem by checking every possibility mentioned above. The troubleshooting in the steps, as mentioned above, thoroughly takes you through all the issues. Moreover, you will be furnished with the knowledge of what a repair person may need to resolve.