Choosing an outboard motor for a small boat is always about balancing power, weight and reliability. In the segment up to 10 horsepower, the Japanese company Tohatsu has been the undisputed leader for many years, namely its flagship model. Tohatsu M9.9BThis unit has established itself as the “gold standard” for inflatable PVC boats and lightweight aluminum boats, offering owners a unique combination of thrust and economy.
Why is this particular model that's been so compelling to water-engineers? two-stroke The series is designed to meet the most stringent environmental standards, but it has maintained ease of maintenance, and unlike its competitors, it uses an advanced mixing system that minimizes fuel consumption and reduces exhaust smoke, which is critical for long-term fishing.
Owners often note that Tohatsu 9.9 It works surprisingly well even at idle speeds, and this is achieved by balancing the crank-and-rocket mechanism with modern bearings, and if you're planning on using a boat for trolling, or just value the quietness of the water, this motor is a great choice, not requiring complex maintenance.
Technical specifications and design features
The heart of the model is two-cylinder The cylinders have a displacement of 169 cubic centimeters, which, with modern carburetor tuning, allows the claimed 9.9 horsepower to be removed. The cylinder block is designed with an aluminum alloy coating that is resistant to corrosion, which is especially important for use in salt water.
The ignition system here is electronic, without the use of mechanical interrupters, which eliminates the need to adjust the gaps. CDI ignition Capacitor Discharge Ignition provides a stable spark at any crankshaft speed, which ensures a confident start even after prolonged downtime and efficient combustion of the fuel mixture in all modes of operation.
An important element is the cooling system, which is taken through a water intake located in lower unit and forced to pump with a flexible rubber impeller. Thermostat in this model is absent, the circulation is on the principle of an open circuit, which simplifies the design, but requires careful attention to the purity of water channels, especially during the course in overgrown reservoirs.
⚠️ Warning: Never start the engine without a submerged lower unit part in the water or without connecting to the forced water supply system. Working "dry" will instantly dissipate the oils and impeller pump, which will lead to overheating and jamming of the pistons.
For a deeper understanding of the parameters, let’s turn to the summary table of specifications:
| Parameter | Meaning |
|---|---|
| Type of engine | two-stroke, 2-cylinder |
| Workload | 169 cubic centimetres |
| Maximum power | 9.9 hp (7.4 kW) |
| Rate of rotation (WOT) | 4500 - 5500 rpm |
| Lubrication system | Gasoline and oil mixture |
The secret of the durability of the piston group
The pistons of the Tohatsu 9.9 engine have a special molybdenum coating of skirts, which reduces friction and allows the engine to enter operating mode faster, minimizing wear during cold start.
Mixing system and economy
One of the most important features that I am proud of. Tohatsuis the application of the system TLDI (Tohatsu Low Direct Injection) Or, in older and simpler versions, an optimized carburetor with a deflector. The classic carburetor versions of the M9.9B use a deflector intake system that prevents the direct release of fresh fuel mixture into the exhaust pipe.
Thanks to this fuel On average, when driving at half-power (about 3000-3500 revolutions), the engine consumes no more than 2.5-3 liters of gasoline per hour. For a tank of 12-14 liters, this means 4-5 hours of active driving, which for most anglers is an absolute record of autonomy.
The quality of the mixture directly affects the formation of a gas, if you use quality oil and pure gasoline, spark plugs. NGKPlant-mounted candles go for several seasons without replacement, but if you notice a loss of power or difficulty starting, the first thing you should do is check the color of the candle insulator: it should be brick-colored.
Use only special two-stroke oils labeled TC-W3. The use of cheap analogues or oils for air cooling (for chainsaws) will lead to the coking of exhaust windows and loss of compression.
Economy is not just about liters of gasoline, but also the resource of the knots. A properly prepared mixture provides excellent lubrication of crankshaft bearings. Oil film in a two-stroke engine - the only thing that protects rubbing surfaces from destruction, so save on the quality of oil is absolutely impossible.
Modifications: Long and short leg
When buying a motor Tohatsu 9.9 The manufacturer offers two main options: a standard leg (S – Short, 382 mm) and a long leg (L – Long, 505 mm), the choice depends solely on the height of the transom of your boat.
For inflatable PVC boats, where the distance from the cut of the transom to the keel is usually about 38-40 cm, ideally suited short-legInstalling a long lower unit on such a boat will cause the anti-cavitational plate to be too deep, which will create additional water resistance and reduce the maximum speed.
In turn, for aluminum motoboats and boats with high sides is necessary. legIf you put a short motor on a high transom, the propeller will capture air in the excitement, causing cavitation and overheating of the engine due to insufficient water intake, a critical point that cannot be ignored.
- 🚤 Short leg (S): Designed for transom trunks 381 mm (15 inches) high, ideal for PVC boats and shallow-seated flatboats.
- ⚓ Long leg (L): Designed for 508 mm (20 in) high transom vessels, it is used on keel boats and high-landing boats.
- 🔧 Universality: Reworking the length of the lower unit at home is possible, but requires replacing the lower unit itself, the lower unit shaft and sometimes the thrust of the gear shift, which is economically impractical.
Therefore, for lightweight inflatable boats, it is always recommended to choose a short leg if the design of the boat allows.
New engine break-in process
New engine Tohatsu M9.9B It requires a mandatory break-in procedure, and neglecting this step can reduce the engine life by many times, and you need to break-in the piston rings against the cylinder walls and burn the bearings.
It takes 10 hours to produce 3-4 full tanks of fuel mixture. equipment It should be fortified, so it is recommended to add 20% more oil to gasoline than the instructions for normal mode, usually a ratio of 1:25 instead of the standard 1:50.
☑️ Checklist of proper breaking in
During the break-in, it is strictly forbidden to keep the gas handle in one position for a long time, you need to constantly change the speed, allowing the engine to operate in different modes, this prevents the rings from "pouring" in one position and ensures uniform wear of rubbing surfaces.
⚠️ Warning: If the engine suddenly stopped starting during the break-in or thick white smoke with cotton fell from the silencer, stop immediately. There may be a violation of the proportion of the mixture or clogging of the jeeler of the carburetor, which requires immediate intervention.
After the first 10 hours of operation, it is strongly recommended to carry out the first maintenance, which includes replacing the oil in the gearbox (even if it is new, there may be metal shavings from the grinding of the gears) and pulling all external bolt joints that may have weakened from vibration.
Maintenance and typical faults
Despite its high reliability, Japanese The main enemy of any technology is storage. If you're putting a boat away for the winter, make sure you get all the gasoline out of the carburetor or use a fuel stabilizer. The remaining gasoline turns into a resin in a few months that completely clogs the jelly.
The ignition system rarely fails, but spark plugs require periodic cleaning and clearance checks. The optimal electrode clearance is 0.9-1.0 mm. If the gap is smaller, the spark will be weak, if more, there may be missed ignition under load. NGK BPR7ES Or their direct counterparts.
The gearbox is another node that needs to be monitored, and the oil needs to be changed at least once a season or after 100 hours of motoring, and if you see an emulsion (coffee milk oil) on the drain, the seals are broken, and the oil has got water in the gearbox, and you can't operate the motor in this state, the gears will quickly fail.
- 🔥 Overheating: Most often caused by the breakage of the impeller pump or the entry of a foreign object (package, algae) into the water intake.
- 💨 Poor set of turns: May indicate clogging of the fuel filter-settlement or violation of the setting of the carburetor.
- 🔊 Engine knock: It indicates critical wear of crankshaft bearings or rod fingers, requires immediate stop.
Regularly changing the oil in the gearbox and using fresh fuel is 90% of the success in the long and hassle-free operation of your Tohatsu 9.9.
Use special aerosol cleaners to clean the carburettor and fuel system, which effectively dissolve lacquer deposits without damaging rubber seals, and compressed air purging is also a mandatory procedure for annual maintenance.
Comparison with competitors and final conclusions
There are many analogues on the market, such as Yamaha 9.9, Mercury 9.9 But Tohatsu often benefits from higher maximum power in its class and more sophisticated ergonomics, such as the romper being more convenient and the launch system (especially the electric starter in the T version) being softer.
Chinese engines such as the Hidea or Sea-Pro are often copies of this particular Tohatsu model, but the quality of casting and assembly of the original is still higher. Tohatsu It is available in almost any service center, which solves the problem of logistics in remote regions.
In summary, it can be said that Tohatsu 9.9bhp It's an investment in confidence on the water, and it's a motor that will forgive some of the mistakes of a beginner, but it will reward the professional with reliable traction, and it weighs 26 to 27 kilograms (depending on the modification) and makes it easy for one person to handle it without the need for a loader.
If you are facing the choice of the first engine for a PVC boat with a length of 320-360 cm, this option will be the most rational. It will provide glides with two adult passengers and a small load, while remaining quiet enough for comfortable fishing.
What is the best gasoline for Tohatsu 9.9?
The manufacturer recommends unleaded gasoline with an octane number not lower than the AI-92. The use of AI-95 is permissible, but does not provide significant advantages in power, and AI-92 is more stable during storage.
Do I need to warm up the engine before going to plane?
After starting, let the engine run for 2-3 minutes at idle speeds, which is necessary to warm up the piston group and start normal oil circulation in the mixture, which will prevent cylinders from hitting the throttle sharply.
Can the motor be kept in a horizontal position?
Short term (transportation) - you can. But for long-term storage (interseason), the motor must be vertically vertical, horizontally, oil from the gearbox can leak through the omentums, and in the engine, condensate can accumulate in the silencer.