On Monday 07 June 2004 3:28 pm in rec.boats James Gemmill wrote:

According to my local service men I should be able to turn about 4600
RPMs with my 5.0 liter mercruiser. I am only turning 4200 at full
throttle, on plane and empty except for drive and one passenger. My
service guys say I can burn the valves at this rate.

Hmmm --- Transvaal disease.
Your engine will produce about 20% less power at 4000 feet unless
it is turbocharged. The air is thinner so there is less oxygen.

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.


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