On Monday 07 June 2004 7:38 pm in rec.boats Gene Kearns wrote:


Firstly get a finer pitch prop to get your RPM back up.
You should probably use different carburetter jets or different
fuel injection settings for high altitude operation, ask the
manufacturer for advice on this point, it is possible to burn valves
if the mixture is too lean. Some engines run rich enough at sea level
to be OK at 4000 feet, others will run too lean and therefore hot.

An engine at 4000 feet needs less fuel to air.... since the air is
thinner. It will burn less fuel and produce less horsepower.

Unless accounted for, an engine that runs properly at sea level will
likely be too rich at "altitude."

Sorry but you are wrong. For a given throttle opening the same volume
of less dense air passes through the carburettor venturi. The partial
vacuum created in the venturi is smaller, sucking less fuel into the
airstream and thus giving a weak mixture. Thus larger jets are
required at altitude to enrich the mixture.

Fuel injected engines will behave differently, the result will depend
on the amount of intelligence in the control system, the type of
environmental sensors used, and the firmware logic in the controller.
Some will get it right, others will screw up rather badly at altitude.

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