Choosing the first outboard motor is always a balance between power, weight and budget. Japanese Yamaha has been a leader for decades, with a 4-horsepower two-stroke model taking a special place in the manufacturer’s lineup, which has become a benchmark for reliability for owners of small PVC boats and light boats.
Why? Yamaha 4hp two-stroke This is a strong interest, despite the strong promotion of four-stroke models, and the answer lies in the unique combination of traction, ease of maintenance and time-tested design, often chosen by fishermen who need to get to the point quickly and tourists who appreciate the light weight of the equipment.
In this article we will discuss in detail specificationIt's a real fuel consumption and a hidden nuance of operation that is rarely mentioned in the booklets, and you'll learn how this model differs from the competition and what to look for when buying a used copy.
Design features and weight parameters
The two-stroke Yamaha power plant with a capacity of 4 hp is built on the basis of a proven engine with air cooling (in some older versions) or water, depending on the year of release and the specific series, although most modern versions are water-cooling The entire structure weighs only about 19-20 kilograms, making it one of the lightest in its class.
This mass allows the engine to be mounted even on inflatable boats with a transom category "C" without the risk of damaging the cylinders or turning the boat over. For comparison, four-stroke analogues of the same power can weigh 5-7 kg more due to the presence of a lubrication system and a more complex gas distribution mechanism.
⚠️ Attention: Despite the low weight, always fix the motor in an upright position or on a special side during transportation to avoid oil leaking from the gearbox or water entering the cylinders through the exhaust hole.
The body of the motor is made of aluminum alloy with anticorrosion coating. Roompile control It provides precise control of the course, and the built-in emergency shutdown system (through the Leningradka cable or the tiller button) guarantees safety on the water.
Technical specifications and productivity
The heart of the unit is a single-cylinder internal combustion engine with crank-chamber purge, with a displacement of 49.6 cubic centimeters, which, when properly adjusted, allows for a maximum speed of the boat to 25-30 km / h depending on the type of vessel and load.
The ignition system here is electronic, CDI (Capacitor Discharge Ignition), which eliminates the need to adjust the gap of candles or monitor the status of the interrupter contacts, as in the old magdinos. significantly improves reliability Start in wet weather and after a long downtime.
The secret of high traction at low speeds
The two-stroke cycle of the engine provides a sharper response to the gas handle than the four-stroke counterparts. Since the working stroke is made every turn of the crankshaft (rather than one, as in four-strokes), the engine quickly enters the plane mode with full load.
The most important parameter for many users is the gear ratio of the gearbox, which is 2.08 (27:13) for the Yamaha 4 hp, which means that there are just over two propeller revolutions per crankshaft revolution, a ratio that is tailored to balance the balance between the two wheels. speed and torque.
| Parameter | Meaning | Units of measurement |
|---|---|---|
| Type of engine | two-stroke, 1 cylinder | - |
| Workload | 49.6 | cm3 |
| Maximum power | 4.0 | hp (kW 2.9) |
| Rate of rotation (WOT) | 4500 - 5500 | min |
| Launching system | Manual starter | - |
| Fuel tank capacity | 1.2 (built-in) / 12 (external) | litter |
Fuel consumption and preparation of fuel mixture
One of the main issues that concern owners of two-tacters is petrolFor the Yamaha 4 hp, it is one of the lowest in the class. On average, when driving in semi-load (about 20-25 km / h), the engine consumes from 1.2 to 1.5 liters of fuel mixture per hour.
However, unlike four-stroke engines, you can't just pour gasoline in here. You have to strictly follow the ratio of mixing oil and gasoline. Usually the manufacturer recommends a ratio of 1:50 (20 ml of oil per 1 liter of gasoline) when using Yamaha's branded oil two-stroke Oil. If you use oil from another manufacturer, the ratio can be 1:25 or 1:30, which is the ratio of the oil of the manufacturer. critically consider.
Use only fresh fuel mixture. Gasoline with the addition of oil (especially mineral) when stored for more than 2-3 weeks begins to delaminate and oxidize, which can lead to clogging of the gillers of the carburetor with resins.
To prepare the mixture, it is better to use a separate canister with a measuring scale, first pour half the desired volume of gasoline, then add the full amount of oil, the container is shaken, and only then add the remaining gasoline for the final stirring.
Refrigeration and maintenance system
The engine is cooled by force with water, which is taken from the reservoir through the water intake hole and pumped through the cylinder shirt. pump-pump (rubber impeller), which is sensitive to work "dry".
Regular maintenance includes changing the gearbox water (at least once a season) and checking the spark plug status. The candle is recommended to be twisted and inspected every 50 hours. The color of the coar on the electrode will tell you about the quality of the mixture: brick shade indicates the norm, black indicates over-enrichment, white - about overheating.
☑️ Seasonal maintenance of the Yamaha engine 4 hp
⚠️ Attention: Never run the motor out of water without connecting to an artificial water supply system ("ears"). The pump without water for even 10-15 seconds can deform the rubber impeller, which will overheat the engine next time.
Comparison: two-stroke Yamaha vs. four-stroke analog
Many buyers fluctuate between two-stroke and four-stroke. Yamaha 4hp 2T loses 4T in environmental friendliness and noise levels. The four-stroke motor is quieter, requires no mixing and emits fewer harmful substances.
But the two-stroke model has some advantages: it's lighter, cheaper to repair, and most importantly, it can be transported in any position (albeit lying on its side in the trunk) without fear of oil leaking out of the crankcase. The four-stroke requires strictly vertical transport.
In addition, the two-stroke Yamaha 4bhp often has a more "roaring" start from the spot, which is important for overcoming overgrown areas or strong currents.
Choose a two-stroke engine if you want mobility, the ability to carry in the trunk of a passenger car and the minimum weight. Choose a four-stroke one if the priority is silence, low-speed economy and no exhaust odor.
Setup of the carburetor and elimination
The regular Yamaha carburetor is set up in the factory, but over time or changing operating conditions (height above sea level, temperature) may require adjustment. The main screws are the quality screw of the mixture (L) and the number of screws of the mixture (H), as well as the idling screw.
If the engine stalls when the valve is sharply opened or does not hold idle revs, most likely, the setting of the quality of the mixture at low revs has lost. The screws should be twisted in 1/8 rotation increments, recording changes in the operation of the engine.
The order of the initial setting (basic values):1. L screw (low revs): twist 1.5 - 2 revolutions from the stop.
2. screw H (high revs): twist 1.0 - 1.25 revolutions from the stop.
3. Start the engine, warm up.
4. Adjust the screw L for stable singles.
5. check the acceleration (there should be no failures).
A common problem is also clogging of the fuel filter-sludge, and if the engine stalls under load, first check the transparent filter bulb at the bottom of the carburetor for water or dirt.
Frequently Asked Questions (FAQ)
Which petrol is best used for Yamaha 4 hp two-stroke?
It is recommended to use unleaded AI-92 or AI-95 gasoline, the main requirement is freshness of fuel, the use of gasoline with an octane number below 90 can lead to detonation and overheating of the piston group.
Which oil is better to cast: mineral or synthetic?
For two-stroke engines, Yamaha is optimally suited semi-synthetic or synthetic oil labeled TC-W3. It provides better lubrication at high revs and burns with less carbon monoxide than mineral oil.
Can this motor be used on a boat 4 meters long?
For a boat with a length of 3.6-4.2 meters with one fisherman and equipment, 4 hp will be enough to go to the planing (speed about 20-22 km / h). If the load is full (2 people + cargo), the boat will go in displacement mode at a speed of about 8-10 km / h.
Why does the engine smoke at idle speed?
Blue smoke on singles is normal for a two-stroke engine, especially if the proportion of oil in the mixture has been increased or the oil is mineral. If the smoke is black and caustic, this indicates an over-enriched mixture or problems with ignition.