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Yamaha 40 HP 4 Stroke Problems – Professional Maintenance Tips

Yamaha 40 HP 4 Stroke Problems

Did you just get yourself a new Yamaha outboard with a 4-stroke motor? Then you could be wondering what sort of problems you can run into with this. We’ll help you identify the problems.

So, what are the Yamaha 40 hp 4 stroke problems?

After some painstaking research, we’ve come to the conclusion that there are 5 common ones. To begin with, you could have issues with the carburetor. Or, your starter can get faulty or have problems with the CDI. Other problems like fuel system failure and lubricating failure are also quite common.

This is just a brief description of the 5 common problems that you might face. Are you interested in knowing about them in detail? Just scroll down and read the article.

Common Problems That You Can Face With A Yamaha 4 Stroke Motor

There are a lot of problems that one can face while using an outboard 4-stroke Yamaha. Not all of them happen to everyone though.

Among those problems, there are 5 that stand out. These 5 problems are mostly faced by people. We’ve also provided you with the solutions for your convenience.

Without any further delay, let’s see what problems you might face:

1. Problems With The Carburetor

Outboard motors are usually built fuel injected or they use carburetors. The 40 outboards built by Yamaha have been built with both for many years now. But, nowadays they’ve been sticking to the fuel-injected versions.

The purpose of the carburetor is to mix fuel and air in the right amount. This mixture of air and fuel gets sucked inside the engine. Then it makes the engine run.

Carburetors in engines with low horsepower like this one need to run more often than others. You need to run them more specifically during the summer. But microbes grow inside fuel when the fuel sits for too long in summer.

These microbes can clog the internal workings which can cause the valves to fail. A failing valve can let in an inappropriate amount of air or fuel into the engine. This can also happen due to dirt.

This issue can be the cause of various other problems. Like engine misfiring when at high speed, engine shutting down frequently, rough rides, and many more. But, you can learn how to start an outboard motor that has been sitting.

A lot of the 40 outboard motors built before 2010 had clogging problems. The design of the motor made cleaning them relatively harder. In most cases, people just had to replace the motors. This is the major reason why they shifted to fuel-injected motors later on.

2. Problems With The Starter

An electric starter can have problems for several reasons. The most common reason is that you have damaged wiring. You’ll be able to identify that quite easily by just inspecting the wires visually.

There are two other problems that usually occur. One of them is a busted fuse. To check if your fuse is alright, take off your electrical cover first. Then take out the fuse holder using pliers. If it looks like the connection is broken, then you have a busted fuse.

If your fuse is okay though, there could be an issue with your battery. Disconnect the battery and clean out the terminals. Recharge your battery and put it back inside.

If it still doesn’t start, then we’re afraid you’ll need a professional to get it looked at.

Capacitor Discharge Ignition (CDI) Failure

3. Capacitor Discharge Ignition (CDI) Failure

The first question that might come to your mind is what is a Capacitor Discharge Ignition. Well, it’s a part of your motor. And the failure of CDI is not uncommon at all. These failures can cause your motor to stall, run roughly, and even misfire at times.

These things have the ability to store information. Which can be later seen from a computer. This way, it’s easy to identify whatever the problem is.

If you’re required to replace the CDI just in case, get the help of a professional.

4. Failure In The Fuel System

There are two fuel pumps, two fuel filters, and a high-pressure fuel rail on an outboard 40. There is also one Vapor Separator Tank (VST) and a VST filter. A fuel system failure can be caused by problems in any one of them.

These are complex stuff so don’t try to do this by yourself. But, a Yamaha fuel pump problem is not that hard to fix though. You can do it by yourself.

Outside the motor, the problem could be at the connectors, tank hose, or even the priming bulb. Problems in any one of them can be identified with a light visual inspection.

5. Failure Lubricating The Oil In The Cylinder

You can face this problem if you have a clogged oil filter. Or, if your oil injection system goes bad.

Your pistons will run dry and they’ll expand and stop working. Basically, the pistons will get stuck. This repair is quite expensive. It’s best if you let the pros do the work on this.

These are just about all the problems that can occur. In some cases, you’ll need to replace something or call a professional. But, if you’ve something broken and it needs to be bonded, try marine tex or jb weld.


FAQs Yamaha 40 HP 4

1. How long can a Yamaha 4 stroke last?

Big 4 strokes can be good for about 5000 to 6000 hours. That is called the high hours of a motor.

2. How often should I service my 4 stroke motor?

Servicing a 4 stroke outboard motor after 500 hours of use is ideal.

3. How fast can these motors go?

The max record is 55 km/h. The average speed is however 40 km/h.

4. How often should you change the oil in a Yamaha 4-stroke outboard?

When you change the oil in your Yamaha 4-stroke outboard, you want to do it at least every 100 hours. If the oil looks dirty or has chunks in it, then you should change it sooner.

5. Which lasts longer a 2-stroke or 4-stroke?

2-stroke engines typically last longer than 4-stroke engines because they use a single cylinder that is not as complex mechanically. Additionally, 2-stroke engines typically use less oil and require less maintenance.

If you want to buy another penta you can read about the comparison of Suzuki 4 Stroke Outboard vs Yamaha.


Well, this is just about all the Yamaha 40 hp 4 stroke problems. For fixing some of these problems, you’ll need the help of a professional.

If you see anything outside these problems, just call a professional.

Good Luck!

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