Welcome to the

Outboard Guide
Give us feedback
Subscribe to our newsletter

When an engine has a vacuum leak extra air is being added after the fuel mixture thereby making the engine run lean. A common example of a vacuum leak is when the carburettor isn't bolted tightly to the engine block and air is sucked in through the small gap. With four stroke engines there can also be cracks or gaps in the intake manifold and with two stroke engines there can also be failed crank seals.