Choosing a power unit for a small vessel is always a compromise between power, weight and cost of operation. In the segment of engines with a capacity of about 10 horsepower, it is a stand-alone stand-alone stand-alone. Yamaha 9.9The engine, which has been the benchmark for reliability and traction for many years, is often called the “middle ground” for inflatable boats and light aluminum boats, as it combines enough power to plane and acceptable weight.
Many owners are considering this model because of the unique ability to unlock software up to 15 horsepower, which makes the purchase even more attractive from an economic point of view. Yamaha 9.9 It is famous for its unpretentiousness to fuel quality and the ability to confidently bring even heavy PVC boats with two passengers on board to the plane. In this article, we will examine in detail all the modifications, technical nuances and secrets of operation of this legendary two-stroke.
Technical specifications and design features
At the heart of the model is a two-stroke two-cylinder engine with a volumetric carburetor, the power unit design has been tested for decades, which ensures high maintenance even in the field, with a displacement of 246 cubic centimeters, and an ignition system. CDI (electronic ignition with condenser discharge) guarantees stable start in all weather, an important feature is the presence of a separate lubrication system, which saves the owner from having to manually mix gasoline with oil in the tank, if the appropriate modification or metering system is used.
The weight of the motor varies between 36 and 38 kilograms depending on the length of the lower unit, which is large enough to carry alone, but quite acceptable for a medium-sized boat to be mounted on a transom. Yamaha 9.9 It is equipped with an efficient water-cooled system with forced circulation, which allows you to work at full speed for a long time without the risk of overheating.
What is the secret of Yamaha 9.9 reliability?
The secret lies in the simple but efficient design of the Mikuni carburetor and the absence of complex electronics that often fail in four-stroke counterparts. The simplicity of the two-stroke cycle is perfected here.
It is worth noting the presence of a speed limiter system that protects the engine from exceeding the permissible values when working without load or in the event of a failure of the screw. Also an important safety element is the engine emergency shutdown cable ("death button"), which should always be at the helmsman's fingertips. Long leg (L) modifications have a 508 mm lower unit, which is optimal for boats with a transom height of 510 mm.
Comparison of modifications: 9.9 vs. 15 hp
One of the most common questions when choosing is the difference between the base version of the 9.9 and its 15 horsepower enhanced version. It's actually the same engine, but with different carburetor settings and limiters. Yamaha 9.9 It has a software restriction that does not allow to develop full power, which makes it legally available for driving without the rights of category "M" (depending on the legislation of the country and the total power of all engines).
The 15 hp model features a more aggressive fuel mix adjustment and the switching restrictions removed, which gives a speed gain of 5-7 km / h, which is critical for heavy boats or when driving against the current. However, it is worth remembering that operating the engine in 15 hp requires better fuel quality and careful control of temperature conditions.
The table below compares key parameters to understand performance differences:
| Parameter | Yamaha 9.9 GMHS (9.9bhp) | Yamaha 15 FMHS (15bhp) | Units of measurement |
|---|---|---|---|
| Maximum power | 9.9 | 15.0 | hp |
| Maximum revolutions | 5000-5500 | 5500-6000 | min |
| Fuel consumption (max) | 5.5 | 7.0 | l-hour |
| Recommended screw | 9.5 x 10 | 9.25 x 10 | lens |
The choice between these two options depends solely on your goals. 9.9 hp It's going to be a more economical and quiet solution, and for full-load water walks or shallow waters where you need to be agile, you'd better consider a high-power option.
Rotor selection: impact on speed and traction
The propeller is a propeller that turns engine power into motion. Yamaha 9.9 It's a 10 inch, 9.5 inch propeller, a versatile solution that allows for a good start and a steady plane, but it often requires a change of propeller to optimize the engine for a particular boat.
If the motor does not reach maximum speeds (5000-5500 rpm) with the fully open throttle, this means that the screw is too heavy (big pitch or diameter), in which case the engine is running in overload mode, which leads to increased gas on candles and pistons. Conversely, if the revolutions exceed the recommended speed, the screw is too “light”, and you lose traction and speed.
- 🚤 For heavy PVC boats with 3-4 passengers, it is recommended to reduce the propeller pitch to 9 or 8.5 inches to improve acceleration dynamics.
- 🏎️ For lightweight aluminum boats and achieving top speed, you can try 11-inch increments screws if the engine is confidently spinning.
- ⚙️ Stainless steel screws are (optional) stronger than aluminum and have thinner blades, which increases efficiency, but they are more expensive and more difficult to repair.
When changing the screw, always use a new screw nut and a locking washer. Reusing old stoppers can lead to the loss of the screw on the water.
The procedure for replacing the screw is simple: you need to unscrew the screw with a key from the kit, pre-lock the screw with a wooden bar so that it does not turn. Be sure to lubricate the shaft with solidol or lithium lubrication before installing the new screw to avoid faltering. Yamaha 9.9 It has a standard seating position that is compatible with propellers from many third-party manufacturers, such as Solas or Michigan Wheel.
break-in and first maintenance
Proper breaking in is the key to a long life for your two-strokeThe new engine has rubbing surfaces that have to get rubbed together. Yamaha 9.9 It takes 10 hours to run. During the first 10 hours, it is not recommended to open the throttle more than 50% (about half the stroke of the gas handle).
After the first 10 hours, you need to replace the oil in the gearbox and perform the first maintenance. This includes checking the spark plugs, cleaning the air filter and checking the tightening of all bolt joints, especially the diewood fasteners and strubcines. Vibration in the first hours of operation can weaken the threaded joints, so this step is critical.
☑️ Checklist of the first TO
⚠️ Attention: Never run the motor out of water or without sufficient coolant flow for longer than 10-15 seconds. Dry friction instantly destroys the impeller of the water pump and can lead to deformation of the cylinder head.
To flush the cooling system after operation in salt or dirty water, use special adapters ("ears") and supply fresh water at a low pressure. Start the engine for washing should be at low speeds so that water can fill the system without forming air traffic jams. Regular maintenance prolongs the resource Yamaha 9.9 It's up to a few thousand hours.
Fuel consumption and efficiency of operation
Two-stroke engines are traditionally considered more voracious than four-stroke engines, but modern models such as the two-stroke engines are more expensive. Yamaha 9.9The average fuel consumption at cruising speed (about 30-35 km/h) is about 3-4 liters of gasoline per hour. When driving in economical mode ("traction, about 20 km/h), the flow can be reduced to 2-2.5 liters.
For the preparation of the fuel mixture, you need to use high-octane gasoline (AI-92 or AI-95) and high-quality two-stroke oil with markings. TC-W3The mixing ratio for a break-in motor is usually 1:50 (1 liter of oil per 50 liters of gasoline), however, for new engines or for heavy use, manufacturers often recommend 1:40 or 1:33.
- ⛽ Use only fresh gasoline, which shelf life does not exceed 1-2 months, as the old fuel is oxidized and loses its octane number.
- 🧪 Thoroughly mix the gasoline and oil in a separate canister before pouring into the tank, do not pour the components directly into the engine tank.
- 🛢️ Add stabilizers to the fuel mixture if you plan to keep the boat with fuel in the tank for more than a month, this will prevent stratification and the formation of resins.
The economy also depends on the condition of the propeller and bottom of the boat. Swallowing or denting the propeller blades can increase fuel consumption by up to 20%. Regular inspection of the underwater part of the boat and propeller helps to maintain the safety of the propeller. fuel-efficiency at a high level.
Typical malfunctions and methods of their elimination
Despite its high reliability, Yamaha 9.9 It's not immune to problems, especially when you're in trouble, and one of the most common problems is having trouble starting or idling at idle speeds, and most often it's contamination of the carburetor or spark plugs, and two-stroke engines are sensitive to oil quality, and can coke in when you use cheap lubricants.
Another common issue is overheating. If the control trickle of water does not go or becomes very weak, you need to immediately turn off the engine. The causes can be in a clogged hole of the control drain (often filled with sand or algae), a malfunction of the thermostat or wear of the impeller pump.
⚠️ Attention: If you experience a knock or vibration different from normal, immediately stop moving. Continuing work can lead to the twisting of the rod liners and major repairs to the engine.
80% of problems with the start and operation of the two-stroke engine Yamaha 9.9 are related to the quality of the fuel mixture and the condition of the spark plugs.
To diagnose ignition problems, you can use a sparkmeter or simply twist the candles and check for a spark by mass. If the candle is black and wet, the mixture is too rich (a lot of oil or air is not enough). If the candle is white, the mixture is poor, which is dangerously overheating. The normal color of the candle insulator is brick-brown. Adjusting the carburetor Yamaha 9.9 requires precision and is usually carried out by screws of quality and quantity of mixture, the position of which is already set up optimally by the plant.
Cost of ownership and final recommendations
Purchase Yamaha 9.9 The initial cost of the engine may be higher than some Chinese counterparts, but liquidity in the secondary market and durability completely compensate for this. Yamaha engines are slowly losing value and are in stable demand. Consumables (candles, oil, filters) are available at any boating store.
When choosing between a used and a new engine, it is worth carefully examining the condition of the lower unit for deep bullies and checking the compression. A good used one can last for many years. If you plan to operate actively in difficult conditions, having a service network in your area will be a decisive factor in favor of an official dealer.
Can I use Yamaha 9.9 for trolling?
Yes, you can. The engine has a stable low revs. It is recommended to use a small pitch screw or a special trolling screw for trolling, and you may need to refine the rummule to fix small turns, since a regular idle lock can give too high speed for some types of fishing.
Which petrol is better to pour: 92 or 95?
Yamaha 9.9 engines are designed to work with AI-92 gasoline. Using AI-95 is permissible, but does not give an increase in power, and in some cases, due to various additives, can more quickly disable candles.
Do I need to drain the oil from the gearbox for the winter?
Pouring oil from the gearbox for the winter is not necessary unless it has changed its color to milk (which indicates water intake). However, if you plan to store it for a long time, it is recommended to replace the oil in the gearbox before canning to eliminate corrosion of internal parts from possible condensation.
Is it true that the Yamaha 9.9 can be swelled to 15 hp on its own?
Technically, it is possible (replacing the limiter in the switch and the carburetor jellies), but such actions remove the warranty and can lead to accelerated wear of the piston group if you do not monitor the quality of the mixture and temperature. In addition, legally the motor will remain 9.9 hp in the documents, which may cause questions for GIMS inspectors when checking the technical specifications.