outboard motor Yamaha 2 CMHS It is a compact but powerful unit that has been in demand for small boat owners for decades, and is popular for reliability, economy and ease of maintenance. 4 metersIt provides them with excellent maneuverability and sufficient speed.
In this article, we will discuss specification models, hers strengths and weaknessesand also give practical advice on operation, repair and tuningWe will pay special attention to the questions that most often arise from owners: how to run the engine correctly, what oil to use, and why. Yamaha 2 CMHS Sometimes it sneezes at idle speeds.
If you're just planning to buy it, or if you're already a lucky owner of it, it can help you avoid the typical mistakes and extend the life of the engine. The Mercury 2.5M and Tohatsu M2.5B are the closest competitors.Based on real tests and reviews of water motors.
Yamaha 2 CMHS Technical Specifications: What's Under the Hood?
Model Yamaha 2 CMHS It's a series of compact two-stroke manually started engines, and its heart is a single-cylinder engine with a volume of one. 76 cm3developing maximum power 2 hp upon 5000 rpmDespite the modest numbers, the engine shows excellent traction at low revs, which is especially valuable for fishermen and lovers of quiet hunting.
Key parameters:
- 🔧 Type of engine: two-stroke, single-cylinder
- 💨 Cooling: air (compulsory)
- ⚙️ gear ratio: 2.08:1
- ⛽ Recommended fuelAI-92 (opportunity to work on AI-95)
- 🛢️ Volume of fuel tank: 1.1 litre (built-in)
- 📏 Weight.: 12.5 kg (no fuel)
The peculiarity of the model is fuel-tankIt simplifies the design but requires refueling every time 40-60 minutes For long hikes, you can connect a remote tank with a capacity to 12 litres through a standard fitting.
The engine's equipped. CDI-ignition (capacitor discharge ignition), which provides a stable spark even at low battery charge (if the electric starter is used in the modification) 2 CMHS EIn the basic version, the cord is used to launch manually.
Advantages and disadvantages: honest analysis
Like any other technical product, Yamaha 2 CMHS It has its pros and cons, and let's look at it based on feedback from owners and expert tests.
Strengths:
- ✅ Reliability: Japanese build quality and materials. With proper maintenance, the engine serves 10-15 years without major repairs.
- ✅ EconomyFuel consumption - everything 0.9-1.2 l/h at maximum speed.
- ✅ Easynessweight 12.5 kg It allows you to carry the motor to one person and install it on a boat without assistants.
- ✅ Ease of repairAvailability of spare parts and understandable design (even a beginner can replace a candle or carburetor).
Weaknesses:
- ❌ Noise: at high speeds, the sound reaches 85-90 dB (Two-tacts are generally noisier than four-tacts).
- ❌ Vibration.: because of the single-cylinder circuit at idle speeds, tremors are possible, which is transmitted to the rumpet.
- ❌ Limited power: for boats longer 4m Or with a heavy load, there may be no traction.
Interesting fact: despite the age of the model (issued with the 1990s), its design remains relevant because of the intelligent engineering base. Yamaha Autolube (in versions with a separate oil) automatically mixes oil with gasoline, which simplifies operation.
If you often swim in salt water, after each exit, flush the engine with fresh water through a special connection, which will prevent corrosion of aluminum parts and prolong the life of the anode.
Motor Running: Why It Matters and How to Do It Right
Many owners neglect the break-in, considering it a waste of time. Yamaha 2 CMHS This stage is critical: it allows the parts to "get lost" to each other, which further reduces wear and increases the engine life.
Step-by-step breaking in instructions:
- Pour the fuel mixture in proportion 1:50 (20 ml of oil per 1 liter of AI-92 gasoline) Use only high-quality two-stroke oil class
TC-W3. - Start the engine at idle speed and let it work 5-7 minutes for warm-up.
- Bring the boat to the water and smoothly increase the speed to 70% of the maximumKeep this regimen up. 10-15 minutes.
- Alternate modes: 2 minutes to 70% power → 1 minute singlesRepeat the cycle. 3-4 times.
- Avoid working at maximum speeds during the first few months. 5 hours exploitation.
Total break-in time 5-10 hours of motorsportThen you can switch to the standard proportion of oil. 1:100 (if the system is used) Autolubeor 1:50 (with manual mixing).
Fill the fuel tank with a fresh mixture | Check the oil level in the gearbox | Make sure there is water for cooling (at the test on land) | Check the motor attachment to the transom | Check the screw for no damage-->
⚠️ Attention: Never run on land without water cooling! 3-5 minutes This can cause the piston to jam, and for the test, use a water barrel or a special stand.
Comparison with competitors: Yamaha vs Mercury vs Tohatsu
To understand how Yamaha 2 CMHS It differs favorably from its analogues, compare it with two popular models of the same class: Mercury 2.5M and Tohatsu M2.5BAll three engines have similar power, but different design features.
| Parameter | Yamaha 2 CMHS | Mercury 2.5M | Tohatsu M2.5B |
|---|---|---|---|
| Max power (hp) | 2 | 2.5 | 2.5 |
| Engine volume (cm3) | 76 | 86 | 85 |
| Weight (kg) | 12.5 | 13.2 | 12.8 |
| Type of cooling | Airborne | Watery | Watery |
| Fuel consumption (L/h) | 0.9–1.2 | 1.0–1.3 | 1.1–1.4 |
What to choose?
- 🏆 Yamaha 2 CMHS The best option for those who appreciate lightness, simplicity and reliabilityPerfect for fishing in quiet waters.
- 💪 Mercury 2.5M - more powerful on 0.5 hpIt is heavier and requires more careful care of the water cooling system.
- 🔧 Tohatsu M2.5B - middle ground: close to the specifications of Mercury, but cheaper to maintain.
The Yamaha 2 CMHS loses to competitors in power, but gains in weight and simplicity of construction, making it a better choice for boaters who often carry the motor by hand.
Tuning and Upgrade: How to Improve Yamaha 2 CMHS
Despite the modest factory specifications, Yamaha 2 CMHS It has the potential to be modernized, and let's look at the most efficient and safest ways to tune.
1. Rotor replacement
Standard three-blade screw diameter 180 mm step-by-step 100 mm may be replaced by:
- 🌀 A screw with a smaller pitch (85-90 mm) It will increase the thrust at low speeds (good for heavy boats).
- ⚡ Four-bladed screw. Improves handling and reduces vibration.
Example: screw Solas 3×8.5×9 It is suitable for most modifications.
Optimization of the ignition system
Installation contactless ignition (e.g. from Yamaha 4CMHS) will increase stability and facilitate the start in cold weather, and you can also replace the standard candle with a lighter light. NGK BR8HS or Champion L86C for better sparking.
Upgrade of the cooling system
To reduce the engine temperature at long loads, you can install an additional radiator This is true in southern regions, where the engine is often at its limit.
⚠️ Attention: Any changes in the design of the engine can lead to loss of warranty (if it is still valid) and increased wear. For example, installing a screw with a large pitch without reworking the engine will reduce maximum speed and create additional load on the gearbox.
How to check the effectiveness of tuning?
After modifications, conduct a water test with a stopwatch:
1. Measure the speed of the boat to its maximum speed.
2. evaluate the behavior of the motor at idle speeds (whether there is vibration or "sneezing").
3. Check the fuel consumption on the standard route.
If the performance improved, the tuning was successful.
Typical malfunctions and ways to eliminate them
Even the most reliable motor can fail over time. Yamaha 2 CMHS and how to address them:
1. The engine won't start.
- 🔋 Reason: The battery (in the version with an electric starter) or a problem with a candle is discharged.
- 🔧 Decision: Check the battery, clean the candle of the sodium, or replace it, and make sure the fuel faucet is open.
2. The engine "sneezes" at idle speeds
- ⛽ Reason: Poor fuel mixture (little oil) or clogging of the carburetor's chicler.
- 🔧 Decision: Rinse the carburetor, check the oil ratio in the fuel, adjust the idle screw if necessary.
3. Engine overheating
- 🌡️ Reason: Clogging of ducts (for air-cooled models) or low oil levels in the gearbox.
- 🔧 Decision: Blow the ducts with compressed air, add oil to the reducer (recommended)
Yamalube Gear Oil 80W-90).
4. Power loss
- 🌀 Reason: Wear of piston rings or damage to the screw.
- 🔧 Decision: Measure compression (norm - 8-10 atmAt low values, the rings need to be replaced. Examine the screw for dents or bent blades.
Diagnosing complex malfunctions (e.g., problems with CDI-block) It is better to contact the service center, but most breakdowns can be resolved independently with a minimum set of tools.
Storage and Conservation Tips for Winter
Proper conservation Yamaha 2 CMHS And before you get down in the winter, it's going to extend its lifespan by years.
Preparation of the fuel system
- ⛽ Pour the remaining fuel out of the tank and carburetor.
- 🔧 Start the engine and let it work on idles until it stalls (this will remove the gasoline from the system).
- 💊 Add a stabilizer to the fuel tank (e.g.,
STA-BIL) before the last gas station of the season.
Engine protection
- 🛢️ Replace the oil in the gearbox (even if the engine is new).
- 🌬️ Blow the cylinder: twist the candle, add 5 ml of motor oil In the hole and turn the crankshaft by hand.
- 🔌 Take off the candle, clean it and store it separately (or install a new one).
3. Care of external parts
- 🧼 Wash the motor with fresh water and dry.
- 🎨 Apply protective coatings on aluminum parts (for example,
WD-40 Specialist). - ☀️ Keep the motor in a dry, ventilated room, hanging it on the bracket (not on the screw!).
⚠️ Attention: Never store the motor in a plastic bag or sealed case! this leads to condensation and corrosion. Use breathable fabric covers.
Conservation takes no more than 1 hour, but saves thousands of rubles on repairs. Motors that are not canned, often suffer from "sourcing" of the piston and corrosion of the carburetor after the first winter.
FAQ: answers to frequent questions from owners
Can I use the AI-95 instead of the AI-92?
Yeah, Yamaha 2 CMHS It can run on an AI-95, but it doesn't add power, and in some cases it can overheat because of slower combustion. AI-92.
How often should you change the oil in the gearbox?
The manufacturer recommends replacements every time 100 motor-hours or seasonly For heavy use, it is better to reduce the interval to **50 motor hours.
Why does the engine smoke white smoke?
White smoke usually indicates water entering the combustion chamber (through a damaged gasket) or using poor-quality oil.
- Integrity of the gasket under the cylinder head.
- The quality of the fuel mixture (possibly too much oil).
What kind of boat can you get this engine?
The model is suitable for boats up to the length of 4 meters weight up 300 kg (including passengers and cargo) Optimum load 2-3 peopleFor PVC inflatable boats, check the maximum permissible power of the engine specified in the boat's passport.
Where can I buy parts for Yamaha 2 CMHS?
Original parts are sold in Yamaha’s branded service centers as well as online stores (e.g., online stores). boatparts.ru, motorshop24.comFor savings, analogues from Sierra or Michigan Wheel (e.g. screws or gaskets).