On Monday 07 June 2004 11:37 pm in rec.boats Gene Kearns wrote:

On Mon, 07 Jun 2004 20:21:13 +0100, Chris Newport
wrote:

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.

Fuel injected engines will behave differently...

Nope. Not wrong. Trust me, Chris.... not wrong. I am a aircraft
pilot and mechanic....

This is getting interesting, if slightly off topic.
I can say with certainty that we always needed larger jets in the
Ford Lotus Cortinas (1640 twin cam) in the Transvaal compared to
Durban or CapeTown. The issue is complicated by different fuels, 83
octane in the Transvaal and 98 at the coast.

Every aircraft piston engine, carbureted, fuel injected, naturally
aspirated or supercharged(above critical altitude) has some
contrivance to lean the mixture at altitude.

Yes but it is not that simple - for example you need a richer setting
for best power in the climb and leaner for economy in the cruise.
I was taught to adjust for best RPM before takeoff and then adjust
for EGT. Aircraft carburettors are a completely different animal
to the automotive variety which do not have to deal with extememes
of both pressure and temperature as well as such delights as ram air
and carb heating. I never saw a car with a priming pump and dual mags.

And you *need* to use it or you'll foul plugs and soot-up the
engine.... I've fixed far too many fouled plugs from pilots that were
afraid to lean the mixture enough for fear of burning valves.

Having driven a pair of Wasps for many years I appreciate your point
but I assure you that I always managed to keep them running sweet.
Thankfully they were replaced by PT6s which are a lot less tempremental.
[ You will probably be able to figure out which airframe this was, and
thus my probable age, but dont tell the group B-). ]


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