Scrap your two-stroke outboard with a carburetor


A Crescent Marin 4, two-stroke gasoline engine with built-in fuel tank and four horsepower.

Up to a third of the petrol goes straight into the lake and there has been a sales ban since 2007. But there are still 150,000 two-stroke outboards with carburettors in operation.

For those who do not want to be able to talk to their company during the boat trip and have a penchant for literally throwing money into the lake, two-act outboards with carburetors are an excellent choice. There has been a resale ban on the roaring and soupy relic since 2007, but there are still roughly 150,000 engines in operation. This corresponds to roughly a quarter of all boat engines, according to the Swedish Maritime and Water Authority.

A number of authorities and organizations have therefore launched a campaign for Sweden’s boat owners to scrap the current outboards in favor of more environmentally friendly alternatives, for example electric operation. The goal is for more people to hand in their two-stroke engines with carburetors for scrapping.

– Preferably change to an electric motor, a four-stroke or a modern two-stroke if you want a new engine. They have lower fuel consumption, cleaner exhaust gases and a lower noise level than the two-strokes with carburetors, says Lina Petersson, expert in boat environmental issues at the Swedish Transport Agency, in a statement.

One third is not used

Due to their design, two-stroke engines with carburetors release up to 30 percent of the gasoline into the water without burning it. According to the Norwegian Sea and Water Authority, this means approximately 2,000 tonnes per year end up in our waterways. Gasoline is toxic and contains, among other things, polycyclic aromatic hydrocarbons that contribute to reduced reproductive capacity and growth as well as cancer.

The reason why two-strokes with carburettors release such a large proportion of the fuel without it being used lies in the construction itself. In a four-stroke there is no opportunity for the unused air/fuel mix to escape through the exhaust valve. Through the more modern direct injection technology, the amount of fuel can also be dosed in a much more precise way than with carburettors, which lowers consumption.

In addition, two-strokes are lubricated by mixing the oil into the fuel rather than being recirculated through a sump as in more modern engines, which means that the oil is either burned or discharged unused. It also leads to the lousy emission values. The automotive industry has long since gotten rid of two-strokes due to the higher emission requirements for passenger cars compared to boat engines.

The two-stroke engine is strong in relation to its weight

The advantage of the two-stroke engine is that it is very strong in relation to its weight, which means that it is still used in, for example, chainsaws. The fact that chainsaws still use carburettors instead of the more efficient direct injection (with a few exceptions) is in turn due to the fuel pump’s size and electrical requirements not being suitable for such a small machine.