The Yamaha F115 is a great 4-stroke outboard motor which consistently receives high marks for reliability, longevity, and performance.
This is due to the outboard’s 1.8-liter displacement and DOHC/SOHC designs with four valves per cylinder, providing a lighter weight and extraordinary volumetric efficiency. This option is the perfect choice for a mid-sized craft, with lots of bang for your buck. Originally put on the market in 1999, the Yamaha F115 has received a number of upgrades since then, improving the basic design with modern features. This suits both water sports enthusiasts and anglers alike.
Like all outboard motors, Yamaha 115 4 stroke outboard problems are bound to occur through heavy usage and aging of components. Despite its high performance, regular maintenance and servicing are required to keep this outboard motor in the water and out of the shop.
In this article, we will take a look at five of the most common Yamaha 115 4-stroke problems, including:
- Faulty head gasket
- Bad fuel pump
- Clogged fuel injectors
- Clogged VST filter
- Trim and tilt switch issues
1. Faulty Head Gasket
Over the lifetime of your Yamaha F115, the head gasket will eventually wear down and fail, causing severe damage to your engine if not addressed.
For novice boaters, the head gasket serves as an important component in the performance and lifespan of your Yamaha F115. Head gaskets are made of a non-porous material located between the cylinder block and the cylinder head (where your spark plugs are screwed in). Its purpose is to seal these parts together to both withstand the compression from the engine while also enabling water to flow between the block and the head for temperature regulation.
Over time, the head gasket of your Yamaha F115 is regularly exposed to a number of elements that reduce its integrity, such as salt water, heat, fuel, and other substances. Once a head gasket fails, water and other contaminants will enter your engine. That leads to poor performance (ie. engine bogging down, excessive vibrations), engine damage, and eventually failure - plus a hefty repair bill.
When it comes to Yamaha 115 4 stroke problems, replacing the head gasket should be a priority every 4 years of service, or sooner if usage exceeds the average boater (50 hours per season, or 200 hours for 4 years). There are also a number of other signs to pay attention to that may indicate faulty head gasket:
- Idle runs too slow/rough
- Low pressure in the cylinders (use a compression test to find out)
- Holes and debris in and around the head gasket
2. Bad Fuel Pump
One of the most common Yamaha 115 4-stroke problems is a bad fuel pump.
There are plenty of signs that you can recognize when a fuel pump has gone bad for your Yamaha F115:
- When a fuel pump malfunctions, the engine may bog down when you throttle up or at idle.
- The fuel pump is responsible for bringing gas from your fuel tank to your engine. Any malfunction can therefore impact consistent performance like RPMs, top speeds, and gas efficiency.
- You may experience Yamaha 115 4-stroke starting problems that often lead to over-priming the engine.
- And when the fuel pump finally gives out, your motor is essentially dead in the water until it is fixed.
Luckily, replacement of a bad fuel pump on a Yamaha F115 is simple repair. It's also relatively inexpensive when compared to other necessary engine repairs.
Tips for Preventing a Bad Fuel Pump
There are a number of things you can do to keep your fuel pump in decent shape:
- Never let the gas tank hit empty. Instead, you should view ¼ full as empty
- Use low-ethanol gas when possible
- Add fuel stabilizer when refueling and winterizing
- Regularly clean out your gas tanks to prevent contaminants from being introduced into your engine and strain the pump
- Drain your gas tanks and hoses during the winter
- Regularly clean and replace all fuel filters, including the VST filter (see below)
3. Clogged Fuel Injectors
Many Yamaha 115 4-stroke problems such as starting issues and misfires can come from clogged fuel injectors.
Fuel injectors can become clogged due to carbon build-up that prevents a smooth distribution of fuel. When this occurs, your outboard may misfire, vibrate excessively, and bog down during idle or when throttle is applied.
As part of keeping your Yamaha 115 4-stroke problems to a minimum, cleaning your outboard fuel injectors with fuel injector cleaner will keep your motor performing at its best.
Repairing Clogged Fuel Injectors
To give you an idea of what tasks, tools, and equipment you will need with a DIY project, here’s what’s involved when cleaning your fuel injectors:
- First, you’ll need to remove the fuel injectors off of the engine, which includes the fuel rails. (Note: There are other methods of cleaning your fuel injectors that enable you to perform this repair while the fuel injectors remain on the engine).
- Carefully remove the rubber O-rings and gaskets from each fuel injector.
- Once removed, manually clean the injectors with a rag and fuel injector cleaner to remove any surface debris.
- Next, you will take a length of fuel hose and clamp the fuel injector to one side of the hose.
- Fill the fuel hose with an ample amount of fuel injector cleaner.
- On the other side of the hose, you will clamp it to an air compressor to create an imitation of the pressure in the engine and force the fuel injector cleaner through the injector’s nozzle. (Note: There is specialized equipment for this task)
- Supply power to the injector to allow the air and fuel injector cleaner to move through the nozzle using a battery and a pair of spade connectors
- Apply air pressure to the hose and quickly tap on the battery to send voltage to the fuel injector, opening and closing it (to simulate its regular function). This enables the fuel injector cleaner to flow through the fuel injector.
- Repeat the process until each of the fuel injectors have been cleaned.
As you can see, this can be a DIY project as a quick fix for those with the tools and the time, but it’s recommended to bring your fuel injectors in for a professional cleaning. Boat mechanics have specialized tools and can perform a more thorough cleaning. However, this is a common repair before and after boating seasons, so many mechanics will require you to leave the injectors with them for a few weeks in order to clean them.
4. Clogged VST Filter
Almost equally important for avoiding Yamaha 115 4-stroke problems to your fuel system is regularly replacing your VST filters. Your VST filter is responsible for keeping contaminants from entering your Yamaha outboard’s Vapor Separator Tank (VST). This is attached to the fuel pump - see above.
Just before gas is pressurized into the fuel injection rails, the VST is the last line of defense against contaminants before reaching the fuel injectors. This means that contaminants that aren’t filtered out by other fuel filters of your engine reach the VST. That makes it a prime spot for deposits to gum up your engine. Sometimes, changing the other fuel filters may not have an effect without this essential maintenance.
There are plenty of kits to help clean and/or replace your VST filter for proper fuel system maintenance. If this maintenance isn’t performed regularly, you may have to perform a more time-intensive and expensive repair that involves cleaning out the Vapor Separator Tank - or worse, installing a replacement altogether.
5. Trim and Tilt Problems
Are you having problems with the trim and tilt switch of your Yamaha F115?
Contrasting with the internal engine problems we've covered so far, trim and tilt problems are external. Trim and tilt involves how well your boat is propelled through the water by the angle of the propeller shaft relative to the boat. A faulty trim and tilt switch can prevent you from the fine-tuning (trim) and dramatic changes (tilt) needed for optimal performance of your Yamaha F115, including:
- Poor gas efficiency due to friction/drag of the water
- Lower RPMs, acceleration, and overall top speed
- Less accurate control during operation
- Inability to raise the motor for storage, servicing, and/or removal
Luckily, you can avoid these problems by swapping out the trim and tilt switch as needed. However, keep in mind that a faulty trim/tilt switch can be a sign of some other issues, such as low battery, electrical shorts, malfunctioning hydraulic motors, and more.
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As you can see, there are many reasons why you may be experiencing Yamaha 115 4-stroke problems. If you’re looking to get to work on maintaining your Yamaha F115 4-stroke problems, Yamaha has plenty of manuals for this outboard (and nearly any other equipment they produce). And to make it a cinch, PartsVu’s Yamaha F115 20-hour maintenance kits and Yamaha F115 100-hour maintenance kits help to deliver on this reliability year after year.
