Choosing an outboard motor for a small boat or inflatable boat is always about finding a balance between power, weight and reliability. Tohatsu outboard motor 25 For years, it has been considered a benchmark in its class, offering water technology owners time-tested Japanese engineering, a model popular with fishermen and outdoor enthusiasts for its ability to confidently glid boats 3 to 5 meters long.
Unlike many competitors, engineers are Tohatsu (Japanese name) MFS25 for four-strokes and M25 The engine is often chosen by those who value self-service and the availability of parts in remote areas, and it is worth noting that this motor often becomes a "donor" for rework, because its design allows for for forcing and upgrading.
In this article, we will discuss in detail the technical nuances, fuel consumption and real life of the unit. You will learn how the American assembly differs from the Japanese (in older models), how to properly break-in and why engine weight of 41-48 kg It's one of the lowest-grade 25-horsepower engines in the class, and it's not just a technical specification, it's a key factor in transportation comfort.
Technical specifications and design features
Analyzing specificationYou need to decide on the type of engine, because Tohatsu produces both versions. MFS25 It weighs about 64 kg (depending on the year of production and the length of the lower unit), making it heavier than a two-stroke counterpart, but significantly quieter and more economical. M25BDS lighter - its weight is about 41-45 kg, which is critical for PVC inflatable boats, where each kilogram on the transom affects driving performance.
The ignition system in modern models is based on CDI (Capacitor Discharge Ignition), which provides a stable spark even at low revs. This is especially important for trolling, when the engine is running at minimum thrusts. The gearbox is made of a durable aluminum alloy and the gear ratio is 2.08:1, which allows you to use screws with high pitch efficiently.
The cooling system deserves special attention. The water intake is located so as to minimize the risk of clogging with algae, but at the same time provides sufficient water pressure through the water supply. pumperThe thermostat in the four-stroke versions helps to get to working temperature faster, reducing the wear of the piston group in the cold season.
Secret of marking
Japanese Tohatsu engines are often labeled "Made in Japan" on the cylinder block, while models for the US market can be assembled at a plant in Virginia, but by Japanese quality standards.
Below is a comparative table of the main parameters for the two most popular modifications:
| Parameter | two-stroke M25BDS | four-stroke MFS25 |
|---|---|---|
| Workload | 432 cm | 432 cm |
| Maximum speeds | 5000-6000 rpm | 5000-6000 rpm |
| Lubrication system | Premix (gasoline + butter) | Carter (oil in the pallet) |
| Fuel tank | 24 l (removable) | 12 L (built-in) / 24 L |
| Weight (with screw) | ~43 kg | ~64 kg |
Two-stroke or four-stroke: which one to choose?
The eternal dispute of motorists is especially relevant in the 25 hp class. Two-stroke engine The lack of oil in the crankcase and the complex gas distribution mechanism makes it less sensitive to the rolls of the boat, but you have to put up with the characteristic sound of work and the need to prepare the fuel mixture.
Four-stroke unit (Four Stroke) is much quieter and smoother, it is almost unheard at idle speeds, which allows you to talk comfortably in the boat, fuel consumption of the four-stroke is lower by 30-40% compared to two-strokes of similar power, which at current gasoline prices becomes a decisive factor.
Four-stroke Tohatsu engines are famous for their survivability, but require regular oil change (every 100 hours or once a season), two-strokes are easier to transport - they can be put on the side without draining the oil, which is convenient when transported in the trunk of a car.
Fuel consumption and efficiency of operation
Question fuel-flow For a two-stroke 25 hp Tohatsu, the average full-gas consumption is about 8-9 liters per hour, and when driving in trolling mode or at low speeds, consumption is reduced to 1.5-2 liters.
The four-stroke version is more impressive, with a cruising speed of around 4000-4500 rpm, which is about 5-6 liters per hour, achieved by more efficient combustion of the mixture and no loss of fuel through the exhaust tract, which is typical for two-stroke circuits.
⚠️ Attention: Use of low-quality gasoline with an octane number below the AI-92 can lead to detonation and overheating of the piston group.
NMMA FC-W.
The savings also depend on the right screw: too much stride will cause the engine to run in tension, increasing the flow rate, and too little will not allow you to develop maximum speed. The optimal is the selection of the screw, which is the engine goes to maximum speed (WOT) at full load of the boat.
To save fuel on a four-stroke engine, regularly check the gap in the valves - its violation can increase consumption by up to 20%.
Procedure for proper engine break-in
From how it goes break-inThe manufacturer recommends not exceeding 50% of the power in the first hours of operation, and for two-stroke models, this is also the period when the grinding of the rings and crankshaft bearings takes place.
In the first 10 hours of work, you should avoid long-term work at constant speeds, you need to periodically change the modes: acceleration, pull-out movement, idling, this contributes to the uniform wear of parts and the correct formation of the oil wedge.
☑️ Checklist for break-in
For four-stroke engines, it is critical to replace the factory running oil after the first 20 hours, which can contain the products of primary wear of parts that, if used for a long time, will turn into an abrasive.
Typical malfunctions and methods of their elimination
Despite its high reliability, boat-engine Tohatsu 25 It can be a typical problem, most often owners have a ignition system failure or fuel supply problem, spark plugs can be covered with soak when working long at low speeds or using left-hand oil.
Another common problem is getting water into a carburetor or fuel pump, which is often when you use old fuel tanks or poor-quality hoses, and you start with a visual inspection and a spark check.
If the engine does not develop full speed, it is worth checking the condition fuel-filter And you can blow out the carburetor's jellyplates, and sometimes the problem is that you don't adjust the angle of ignition, which requires a specialist to use a strobe.
⚠️ Warning: If there is a foreign knock or vibration, immediately turn off the engine. Continuing work can lead to the twisting of the rod liners and expensive overhaul.
90% of problems with the start of old engines are associated with the quality of the fuel mixture and the state of the spark plugs.
Carburetor adjustment and idling adjustment
Independent carburetting Tohatsu carburetors usually have two main adjusting screws: a mixture quality screw (Low Speed) and a screw of the amount of mixture or throttle stop (High Speed / Idle).
Adjustment should be carried out only on the heated engine. First, the quality screw achieves maximum and stable idling speeds, and then the number screw sets the desired crankshaft speed (usually 900-1000 rpm).
Procedure:1. Warm up the engine for 5-10 minutes.
2. wrap the screw of quality to the point (not much!).
Turn 1.5 - 2 revolutions (basic setting).
4. Adjust for engine operation.
Incorrect adjustments lead to either overheating (poor mixture) or increased gassing and choking (rich mixture). In modern environmental regulations, factory settings often make the mixture slightly poorer, which may require correction for our operating conditions.
Frequently Asked Questions (FAQ)
What is the best oil to use in a two-stroke Tohatsu 25?
Use only high-quality synthetic or semi-synthetic oils labeled TC-W3Branded Tohatsu oils or proven analogues like Motul, Evinrude will provide better lubrication and less soda formation.
Why does the engine stop at idle speed?
There are several reasons: clogged idle jikler carburetor, air sucking through the gasket of the intake manifold or improperly configured screw quality mixture. Also check the condition of the fuel filter.
Can I keep the Tohatsu 25 engine on my side?
The four-stroke version cannot be stored on the side - the oil from the crankcase will get into the combustion chamber. The two-stroke motor can be transported on either side, but for long-term storage it is better to put it vertically or on a special stand.
Which screw to choose for an inflatable boat 3.2 meters?
For a boat of this size and two people, a 9-10 inch screw is usually suitable. If the boat is loaded (3+ people), a propeller with 8 inches increments may be required for a confident exit to planing.