yamaha-outboard Yamaha outboard motors have been around for quite a number of years. They have a reputation for being very reliable. The Yamaha outboard range is wide – from 2.5hp to 350hp – and most are now 4 strokes. However, they still produce 2 stroke outboards. The range is from 8hp to 25hp and these 2 cylinder outboard engines use a carb loop charge. This Loop Charging increases the combustion efficiency which optimises the performance and fuel economy of the outboard engine. The smaller 8hp engine has cross-flow scavenging which has proved very reliable. On these 2 strokes the fuel to oil mixture is 100:1 which helps to reduce smoke, fumes, odour and spark plug fouling. The mixture is needed to protect the outboard engine and reduce oil costs.

Yamaha outboard motor 4 stroke range starts with their smallest engine – 2.5hp. This is a single cylinder 72cc OHV engine very popular as an outboard on tenders, mostly inflatables. You often see them clamped to the rails of yachts as they are very lightweight, only 17 kgs (37 lbs).  For used yamaha engines go here.

The Yamaha outboard mid range starts at 40hp to 90hp, all have electric start as manual would be too exhausting to do on a regular basis. All use DOHC fuel injection and the microcomputer ignition adjusts the timing to maintain optimum engine performance and economy. From 50hp to 90hp outboard range a multi-port precision electronic fuel injection system is used. This is 4 individual fuel injectors which deliver a fuel and air mixture to each cylinder. The benefit of this arrangement is easy of starting, smooth acceleration and very good fuel economy.

 

Another feature of this range of Yamaha outboards is the composite intake manifold. Each cylinder has a long tube intake track which is tuned to increase the air flow. This increased air flow improves low end and mid range torque performance which results in increased acceleration. In addition the air silencer box reduces the air intake noise.

The high powered Yamaha range of outboards are all V6 4 strokes. 200hp, 225hp and 250hp outboard engines have all the features mentioned in the mid range and also use a single belt drive system. This system uses fewer moving parts with automatic belt tensioners for long term durability. Another new feature is the in-bank exhaust. Yamaha have reversed the conventional 4 stroke configuration which now allows the exhaust to exit between the V block resulting in a more compact design.

Yamaha outboard motor maintenance tips

One of most common problems with Yamaha outboards is excessive smoke when at idle. This often happens when the engine has been idling or trolling for some time. The engine tends to load up with oil at these times. Try changing your routine useage – in other words do not idle for too long.

Other things to consider.

What TCW-3 oil are you using? Always use the manufacturers recommended oil as it provides the best protection and low smoke properties.

The engine temperature also affects the smoke level. Low temperature causes a rich fuel mixture which causes smoke. Make sure your engine is running at the recommended temperature.

Your fuel pump may be faulty – the diaphram may be damaged. Or the floats in the carburettor/VST may be stuck or blocked. Or there may be too much fuel going to the engine, either way it will need fixing.

Change the spark plugs. Adjust the gap in the new ones to the correct clearance.

Look at your service manual and check that the throttle plates are properly synchronised.

Check your engine idle speed. If it set too low it will cause a rich mixture and smoke.

The oil pump link arm may need adjusting. Check the manual for correct specification.

Check that the oil is circulating properly and that there are no blockages or obstructions. Look at all the hoses for damage. Also look at the air box to see if the oil is draining away.

Again with the oil, check the oil tank vent. Make sure the vent line and nipples are not blocked, kinked or pinched.

Another problem may be that the engine oil tank is overflowing into the air box.

Check that the rear seal of the engine oil pump is not leaking.

Finally, test that the engine oil line valve – which is a one way valve – is not stuck partially open.
All these are possible causes of excessive smoke from your outboard. Either do these checks yourself or suggest them to your service mechanic.

For second hand yamaha outboard engines follow this link.

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