The choice of outboard motor for a small PVC boat or an aluminum boat often comes down to power limitations dictated by category rights or the physical parameters of the craft. Tohatsu The MFS9.8B/E/S series is becoming a benchmark for reliability and versatility, not just powertrains, but complex engineering systems that can turn a conventional rowing boat into a full-fledged pleasure boat.
The main feature of this line is its flexibility: the base model is often labeled as 9.8 horsepower, but structurally it allows you to easily and legally (from the manufacturer’s point of view) reconfigure to 8 hp. Four-stroke cycle The work provides a quiet run and low fuel consumption, which is critical for long-term fishing.
Many aquatic motorists mistakenly believe that the difference between modifications is minimal, but this is not quite true. Tohatsu 9.8 This will help you avoid problems with GIMS and extend the life of the engine, and in this article we will discuss in detail the differences in versions, features of service and real performance indicators.
Technical specifications and design features
Engine. Tohatsu MFS9.8 It's based on a time-tested platform that has proven to be one of the most reliable in the small power class, with a cylinder capacity of 163 cubic centimeters, and a SOHC gas distribution system (one camshaft in the block head) that provides stable thrust at low and medium revs. torque This is more important than the maximum speed of the shaft.
The weight of the motor as standard with a 12-volt starter and generator is about 26-27 kg. This makes it easy enough to carry by one person, but also massive enough to extinguish vibrations on the hull of a light boat. The cooling system is built on the principle of water intake through water intakes in lower unit, which requires careful attention to the purity of water.
An important element of the design is the CDI electronic ignition system. It does not require adjustment of candle gaps during operation, but the quality of the spark directly depends on the state of the candle. flywheel For models with electric starter, manual start is also provided, which is a mandatory safety requirement.
⚠️ Attention: When operating the motor in brackish water, be sure to use fresh water to flush the cooling system after each exit. Corrosion of the internal channels of the cylinder block is the most common reason for major repairs of these engines.
Secrets of marking Tohatsu models
In the Tohatsu lineup, the letters at the end of the model name matter. For example, "B" often means long lower unit, "S" means the presence of an electric starter, and "E" means a remote control system or electric start. Always check the product's passport, as visually the 2010 and 2023 models may differ in the location of the control levers.>
What is the difference between 9.8 and 8 hp?
The difference between the 9.8 and 8 horsepower variants is a concern for many buyers, with the engine physically the same, and the difference lies in the control unit software (for injector versions) or the carburetor and the speed limiter (for carburetor versions). Power 8 hp is achieved by artificially limiting the maximum number of turns of the crankshaft.
Why is it necessary? First of all, to comply with the law. In many regions, registration with GIMS is not required for engines up to 8 hp inclusive (if other conditions are met, such as the weight of a boat). Tohatsu 9.8You get the potential to upgrade, but use it in a "strangled" mode.
Switching from 8 to 9.8 hp (re-renewal) doesn't usually require replacing the hardware. It's enough to remove the limiter or reflash the block. However, it's worth remembering that increasing power leads to an increase in the load on the transmission and lower unit. If your boat is heavy, running to the limit of the 8-horsepower version can be even safer for the resource than forcing to 9.8.
Power system: carburetor or injector?
Lineage Tohatsu In this class of capacity, there are both carburetor and injection models, and the carburetor versions are easier to maintain, cheaper to repair, and less demanding on fuel quality, but they are sensitive to temperature changes and may require idling adjustments when parked for long periods.
Injection modifications (EFIs) provide more accurate dosing of the fuel mixture, which has several advantages: easier starting in any weather, no need to pump a pear, stable idling speeds and reduced fuel consumption. Electronic system It adapts to the change in the load and quality of gasoline.
On the other hand, injector diagnostics require a special scanner and knowledge. If the carburetor can be washed and tuned in the field with a minimum set of tools, then electronics are not a good joke. For most amateur anglers, the carburetor version remains the "middle ground" in terms of reliability / price.
Fuel consumption and economy
One of the main arguments in favor of four-stroke engines Tohatsu Unlike the two-stroke brethren, there is no fuel loss through exhaust. The average full-gas fuel consumption (WOT) for the 9.8 hp version is about 2.5-3.0 liters per hour.
When driving in trolling or calm planing mode, the flow rate drops to 1.0-1.5 liters. This allows you to comfortably fish all day on one tank of 12 liters. Comparison with two-stroke analogues shows savings of up to 30-40% of fuel, which, in terms of the season of operation, translates into a significant amount.
Expenditure is directly affected by the state propeller And the bottoms of the boat, and if you throw shells or damage the propeller blades, you increase the drag, you get the engine to run at higher speeds to get the same speed, and you can clean the propeller regularly, and you can save fuel.
Maintenance and maintenance
Regular maintenance is the key to a long life for you. TohatsuThe first oil change in the engine must be made after the first 20 hours (break-in), then the interval is 100 hours or once a season, whichever comes first. FC-W.
Ignition plugs require inspection every 50-100 hours. Candle plugs can tell you about the engine: black soda indicates a rich mixture, white indicates poor or overheating, it is also important to regularly lubricate the points of connection of the control levers and check the tension of the belt (if it is in a particular modification).
☑️ Checklist of seasonal services
Pay special attention to the gearbox. The gearbox oil is replaced annually before the season starts. If you see an emulsion in the leaked oil, it signals water entering the glands. Operating the motor with water in the gearbox will cause the gears to collapse rapidly.
Comparison with competitors
In the small motor market, Tohatsu 9.8 There are serious competitors, notably the Yamaha F9.9 and Suzuki DF9.9. Yamaha often wins in the prevalence of spare parts and liquidity in the aftermarket. Suzuki is famous for its selective propeller shaft system, which allows for better screw selection.
However, Tohatsu Japanese assembly (unlike some Chinese counterparts under other brands) guarantees compliance with tolerances. Tohatsu motors are also often used as a base for Mercury engines, which confirms their high engineering level.
| Characterization | Tohatsu MFS9.8 | Yamaha F9.9 | Suzuki DF9.9 |
|---|---|---|---|
| Workload | 163 cm | 183 cm | 169 cm |
| Weight (with electric starter) | ~27 kg | ~38 kg | ~33 kg |
| Launching system | Manual/Electro | Manual/Electro | Manual/Electro |
| Generator | 12V, 6A (option) | 12V, 6A (option) | 12V, 6A (option) |
Frequent malfunctions and their elimination
Despite the reliability, problems can arise, and one of the common reasons for failure is clogging of the carburetor's jellyplates due to poor-quality gasoline or prolonged downtime with fuel in the system, the solution is simple: disassembling and ultrasonic cleaning of the carburetor, replacing rubber seals.
Another problem is overheating, which can be caused by a break in the impeller of a water pump or by a foreign object getting on the water intake. Temperature monitoring Mandatory: if the control stream of water does not go or is weak, the motor must be immediately silenced.
⚠️ Attention: Never start a motor without water-cooling, even for a few seconds. The pump oil and impeller can melt instantly, and the metal rubbing against the metal will lead to a bully in the cylinder.
Transmission problems are often related to remote control cable or jerk. Shift Cable requires accuracy: improper setting will lead to the fact that the motor will stall when the gear is turned on or will not go to full gas.
Selection of propeller
The right screw is critical to the realization of motor power Tohatsu 9.8The standard propeller has a medium-load pitch, and if the boat is overloaded, the engine will not be able to reach maximum speed, which will lead to overheating and coarseness. If the boat is light, the engine will "twistle" the speed, risking the valves.
The selection is experimental. Measure the revolutions on full gas with full load. The optimal range for this engine is usually 5000-6000 rpm. If the revolutions are lower, you need a screw with a smaller pitch, if higher, with a larger one.
FAQ: Frequently asked questions
Can I increase the power of the Tohatsu 9.8 to 9.9 or 10 hp?
Technically, the 9.8 hp engine is often a de-forced version of more powerful models (e.g., 15-20 hp with a constraint). However, increasing the power beyond the passport (up to 9.9 or 10) requires replacing the carburetor, intake manifold and reconfiguring the ignition, which reduces the resource and can lead to a failure of the piston group.
what oil to use in the Tohatsu gearbox?
Use only transmission oil for outboard motors with viscosity SAE 90 or 80W-90 It is important that the oil contains additives that prevent emulsification when water enters.
Why does the engine stop at idle speed?
The most likely cause is contamination of the carburetor's idle jeckler or air suction through the intake manifold, and it's also worth checking the adjustment of the gas cable and the state of the spark plug. In injection models, the cause may be a malfunction of the throttle position sensor.
Do I need to dilute the oil with gasoline in a four-stroke Tohatsu?
No, absolutely not. The four-stroke engine is filled with oil separately in the crankcase, and the tank is filled with pure gasoline. Mixing the oil with gasoline will lead to rapid failure of the catalyst (if any), candles and piston group due to detonation and coking.