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Why Won’t My Harley Davidson Start When Hot?

Taking your Harley Davidson for a ride is an incredible experience. But it can be a frustrating moment if your Harley Davidson won't start when the bike is hot. Let's take a look at some of the reasons this may be happening.

Here are common culprits for a Harley Davidson that won't start when hot:

  • Bad/dirty spark plugs
  • Failing ignition coil
  • Vapor lock
  • Bad battery
  • Failing ECU

As you can see, there are a few different reasons your Harley Davidson may not start when hot. In this article, we will discuss each one in more detail. In addition, we will answer other frequently asked questions about Harley Davidson bikes, so read on!

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A Harley Davidson parked outside a building, Why Won't My Harley Davidson Start When Hot?

Harley Davidson Won't Start When Hot—What Could Be Wrong?

Harley Davidson bikes are one of the most popular motorcycles on the market. They are well known for their quality and durability.

However, like any other vehicle, they can have problems from time to time. One of the most common issues Harley Davidson owners face is that their bikes won't start when hot.

This can be frustrating when your bike won't start after a long ride on a hot day. But don't worry, let's take a look at the most common causes of this problem.

Bad/Dirty Spark Plugs

One of the most common reasons your Harley Davidson won't start when hot is due to bad or dirty spark plugs. Over time, spark plugs can become fouled with oil, dirt, and debris. This can cause them to misfire, which can prevent your engine from starting.

To clean your spark plugs, you will need to remove them from the engine and clean them with a wire brush. You may also need to replace them if they are damaged.

Failing Ignition Coil

Another common reason for a Harley Davidson that won't start when hot is a failing ignition coil. The ignition coil is responsible for providing the spark that ignites the fuel in the engine.

If your bike is hot and the ignition coil is on its way out, it may not be able to provide the spark needed to start the engine. You will need to replace the ignition coil if it is failing.

You can check the ignition coil with a multimeter. In addition, if the ignition coil is so hot you can't touch it, it is likely failing.

Click here to see this multimeter on Amazon.

Vapor Lock

Another potential issue that could cause your Harley Davidson to not start when hot is vapor lock. Vapor lock occurs when the fuel in the carburetor or fuel injection system boils and turns to vapor. This can prevent the fuel from reaching the engine, which will prevent it from starting.

To prevent vapor lock, you can install heat shields around the carburetor or fuel injection system. You can also add heat sleeves to the fuel lines.

Bad Battery

If your Harley Davidson has a bad battery, it may not have enough power to start the engine when it is hot. This is because the heat can cause the battery to lose some of its charge.

You can check the battery with a voltmeter. If the voltage is below 12 volts, the battery is bad and needs to be replaced.

You should also check that the battery connections are clean and tight. Loose connections can cause the battery to lose power. If you rode a lot in hot weather, it is also a good idea to check the battery acid level.

Failing ECU

Another potential issue that could cause your Harley Davidson to not start when hot is a failing ECU. The ECU is responsible for managing the engine's ignition and fuel injection system.

If a temperature sensor in the ECU is not working properly, it won't send the right amount of fuel to the engine. This can cause the engine to not start when it is hot.

You will need to have the ECU checked by a mechanic if you suspect it is failing.

These are some of the most common reasons your Harley Davidson won't start when hot. If you are still having trouble starting your bike, take it to a mechanic for further diagnosis.

Riders cruising down a small forest road

What Causes A Harley Davidson To Not Start?

Other than the issues stated in the article, there are a few others that could prevent your Harley Davidson from starting in general. These include:

Failing Fuel Pump

Like other vehicles, the fuel pump in a Harley Davidson can fail over time. If the fuel pump is not working, it will not be able to deliver fuel to the engine. This can prevent the engine from starting.

A failing fuel pump can often be diagnosed by listening for a noise when the key is turned to the "on" position. If you don't hear the noise, the fuel pump is likely failing.

Fuel contamination is another issue that can cause a fuel pump to fail. If the fuel has water or debris in it, it can damage the fuel pump. This will prevent the engine from starting.

Harley Davidson bobber

Clogged Fuel Filter

Over time, fuel filters can become clogged with dirt and debris. If the fuel filter is clogged, it will prevent fuel from reaching the engine. This can cause the engine to not start.

You can check the fuel filter by removing it and inspecting it. If it is clogged, you will need to replace it.

Dead Key Fob Batteries

If your Harley Davidson has keyless ignition, the key fob batteries may be dead. This can prevent the engine from starting.

You can check the key fob batteries by opening up the key fob and replacing the batteries.

Clogged Carburetor

If your Harley Davidson has a carburetor, it can become clogged over time. This can prevent fuel from reaching the engine, which will cause the engine to not start.

You can clean the carburetor by removing it and spraying it with a carburetor cleaner. This is typically only on older models of Harley Davidson. Most newer models have fuel injection, which does not require carburetor cleaning.

Bad Fuel Injectors

For newer models of Harley Davidson with fuel injection, bad fuel injectors can prevent the engine from starting.

If the fuel injectors are not working properly, they will not be able to deliver fuel to the engine. This can cause the engine to not start when it is hot.

You will need to have the fuel injectors checked by a mechanic if you think they are bad.

These are some of the other potential issues that could prevent your Harley Davidson from starting. If you are still having trouble, take it to a mechanic for further diagnosis.

Bad Relay Switch

Another potential issue that could prevent your Harley Davidson from starting is a bad relay switch.

The relay switch is responsible for sending power to the starter motor. If the relay switch is bad, it will not be able to send power to the starter motor. This can cause the engine to not start.

You will need to have the relay switch checked by a mechanic if you think it is bad.

Starter Motor Issues

The starter motor is responsible for starting the engine. If the starter motor is not working, the engine will not start.

There are a few issues that can prevent the starter motor from working. These include a bad starter solenoid, a bad starter motor, or a bad starter relay.

Mechanic checking his motorcycle

What Temperature Is Too Hot For A Harley Davidson?

Overheating can cause issues down the road for your Harley Davidson. It is important to know what temperature is too hot for a Harley Davidson so you can take steps to prevent overheating.

Typically, anything over 250 degrees Fahrenheit is too hot for a Harley Davidson. If the temperature gets too high, it can cause engine damage.

The reason being is that at 250 degrees Fahrenheit, the oil starts to break down. This can cause the engine to seize up, which will result in costly repairs.

Unless you are running your Harley Davidson at a track or in hot weather, you should not have to worry about the engine getting too hot.

If you are riding in hot weather and are climbing hills, make sure to take breaks so the engine can cool down.

A modified Harley Davidson bobber

If you think the engine is getting too hot, you can check the temperature gauge on the dash. In the case it is in the red, pull over and let the engine cool down.

How To Cool Down A Harley Davidson?

If your Harley Davidson is overheating, there are a few things you can do to cool it down.

First, turn off the engine and let it cool down for a few minutes. Then, check the coolant level and add more if needed. Next, check for any leaks in the cooling system. If there are any leaks, repair them as soon as possible. Finally, make sure the cooling fans are working properly. If they are not, replace them.

If you follow these steps, you should be able to cool down your Harley Davidson and prevent it from overheating in the future.

Final Thoughts

A Harley Davidson parked outside a building

With any luck, one of these tips will help you get your Harley Davidson started. However, if you are still having trouble, take it to a mechanic for further diagnosis.

Harley Davidsons are a great American-made product, but like anything else, they can have their issues. By being aware of some of the potential problems, you can be prepared and get back on the road in no time.

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