Ottawa john: - Not a great policy with lawnmowers - RPM should be set for blade tip speed - wider cut mowers set to run slower, narrower cut mowers can be set to run faster.
Mowerles: - reducing an engine's operating rpm does not make them last longer - in fact it can *shorten* the life of the engine, as you have more heat and less cooling air volume. Any difference in engine life based on the RPM setting is very negligible at best an hour or two difference over 250 - 500 hours is hardly worth sacrificing performance.
However, setting an engine RPM to higher than factory specs, is a dangerous game as well - for all concerned: look up the engine's RPM specifications in the replacement engine section of parts books for the particular spec number, and set RPM to that spec, which is where it was designed to run to balance performance and safety. - If you are a pro shop and set RPM to a different value than specified for the equipment, you're opening yourself up to a liability lawsuit, so better be sure you have your liability insurance paid up.
Arbitrarily setting the engine's RPM to 3800 when the equipment and engine specs call for 3600 (and all specs are *top no load* meaning - engine standing alone without any other load on it) can very quickly lead to disaster...
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