Air Problems
The engine needs a supply of good quality air to operate properly. For combustion to take place there needs
to be the correct amount of oxygen, petrol and heat. If there is not enough oxygen, the petrol will not burn strongly and
efficiently or will not ignite at all. If there is too much oxygen, the petrol will burn too hot and possibly melt the piston
or not ignite at all.
The air needs to get into the combustion chamber with the petrol, burn, and then get out as exhaust.
Intake air and exhaust gases are considerations.
Blocked and restricted air filters can restrict the flow of air into the outboard engine.
Most outboards don’t have air filters.
The air going into the engine must be fresh. Make sure there are no exhaust fumes getting into the
fresh air supply. The oxygen in this air is depleted and combustion will not take place properly.
2 stroke outboards get the air into the combustion chamber through vacuums and pressures created by
the piston going in and out of the crankcase. Leaking crankcase seals and gaskets, broken and chipped reeds
or just a plain old and worn engine can cause problems with air flow. The down strokes are just as
important as the compression strokes and it is very hard to test for crankcase condition.
Exhaust back pressure is very important for 2 stroke outboards. Modifying the exhaust system can have
unknown and often undesirable results.
Exhaust restrictions. If the air cannot get out then fresh air cannot get in. Ensure there are no exhaust
restrictions.
Air at altitudes above 1000 metres has less pressure on it to push through the carburettor and collect
the correct amount of petrol. Outboards operated at altitudes above 1000 metres and sometimes
even lower may need changes to the main jets. This should only be done by a qualified person.
Incorrect jetting could cause major engine damage.
Electronic fuel injected (EFI) outboards have air pressure compensating sensors that send a
signal to the computer and the computer adjusts the fuel injector opening times to allow for the pressure
difference.
- Contact Cairns Outboard Service for your outboard service requirements.