How to Fix a Honda 400EX That Won’t Start

Before we explore any solution, the First question for you – Is your Starter Motor Working? Depending on your answer, the process of figuring out the solution will be different. We will go through both conditions in this Article.

Starter Motor Doesn’t Operate

First of all, check all the basics things – Is your Ignition Switch Off? Is the Engine stop key in the right position? Is the Transmission in neutral position? If everything is in starting position, read on.

1. Check the Battery Voltage

Once you have made sure that the ignition switch isn’t off, we need to make sure that the battery voltage is between 12.5v and 13v. If the voltage is below this range, you’ll have to manually charge the battery. If your battery is past it’s time, you should consider replacing it.

2. Check the Main Fuse

Often with the 400ex, you will find that the main fuse has blown off due to excess current. In such a situation, you’ll have to change the fuse and you’ll be good to go.

3. Check the Starter Solenoid

If the battery is giving the power, and the main fuse isn’t blown up, the next possible problem is the started solenoid.

The solenoid acts like a switch between the battery and starter motor.

First, you’ll have to check (with a multimeter) whether the solenoid is getting power from the battery. If it’s not getting power, you’ll have to check the wiring that connects the battery to the solenoid.

If you have power going to the solenoid, no audible click, then it’s time to replace the starter solenoid.

The last step is to check the power going out from the solenoid.

If everything is fine with the battery, fuse, and solenoid, then the problem is most likely the starter itself. In that case, you’ll have to replace the starter motor.

Starter Motor works But the Engine Won’t Start

If power is reaching the starter motor but the engine still isn’t starting, then it’s either not getting enough fuel, air, or spark (or it’s getting a spark at the wrong time)

Start with the basic things – check if the ATV has enough fuel and the shut-off valve isn’t closed.

1. Is the combussion chamber getting enough fuel?

When you start your engine and open the throttle, the carburetor mixes the air and fuel in an appropriate amount and passes on the mixture to the combustion chamber where the power is produced by combustion.

If the combustion chamber is not receiving the air and fuel in the correct ratio, it won’t produce the required power.

To test whether or not this is your case, start with spraying a starter fluid while starting the engine. If it turns on, your engine isn’t getting enough fuel for the amount of air that’s getting sucked in.

In such cases, you’ll likely have to clean the carburetor or adjust the carburetor (cleaning the carburetor will usually fix the problem).

2. Too much Fuel

Too much fuel for a given amount of air (aka engine flooding) will wet the spark plug.

To clear a fooded engine, honda’s manual suggests to –

Keep the engine stop switch and the Choke Lever Off, Throttle Fully Open, and press the start button for 5 sec. Then wait a few more seconds before turning the stop switch to the run position.

It is very possible that the carburetor isn’t getting enough air in, which is causing the flooding.

Cleaning all the air holes that connect to the carb might solve the problem of not receiving enough air. You should also check the air filter for any potential problems.

3. No Spark?

If the air-fuel mix is right then you’ll need to check if the spark plug is functioning properly and firing at the right moment. You can use an inline spark tester to test the spark.

4. Compression Issue

If everything is working well, then it is bad news! I.e there is a compression issue. You may refer to this video for compression testing.