diesel motor

[carl]

have an 81 yanmar 15hp that starts good, runs smooth and uses no oil. running the motor all the way up to about 80% throttle the exhaust is clear, 100% throttle it runs smooth but the exhaust appears to get darker. is there a speed governor that just is adding more fuel and no more air or does anyone know what the exhaust color change comes from? thanks ps the last 20% or so throttle yields no more speed, 80% puts the boat a little above hull speed.

 

[Gord May]

dark exhaust 'smoke'

Dark smoke is generally a symptom of diesel engine overload, or in some extreme cases: air restriction (intake or exhaust), excessive valve (top) clearance, fuel injection timing, etc.It sounds (to me) that you attaining “cruising” RPM (continuous) at 80% throttles position. The engine is rated continuous & intermittant (usually 1 hour).