RPM on 100 HP Yanmar

[Mary & Roger]

Has any one noticed any difference between engines rpm? We had our boat pulled, cleaned, props checked, & painted, thinking that would fix the problem of port engine 400 rpm less than starboard. No change!!! Just wondering if the tachometers/ sending units have given problems.

[duetto]

i think surveyors in audience would say you need to check them with an external known tach.

[S Slater]

Hi
When were the filters last changed? Also don't forget that there is a fuel filter on the actual engine itself in addition to the racor filters.
Simon

[Mary & Roger]

Simon, thanks, but all filters were changed about 60 hrs. ago, didn't fix the problem. I am waiting to get RPM measured with a external tach. Roger

[jbrad]

Hi Mary and Rodger,

I had a similar problem on Mr Busy. We have the 75 hp engines not the 100's though. It turned out to be the tachs/harnesses. We checked both engines with a external tachometer reading off the flywheel. It turned out that both engines were within a range of 5 t0 25 rpms depending on the level. The tachs were showing a range from 0 at 2100 rpm up to over 200 rpm difference at the stops. We also have a small difference from the upper and lower helm. It appears that the tachs are not that accurate. We also found a problem with the starboard engine tachs droping off to 1200 from 3600 when testing in a no load condition only ( the engine maintained the same rpm, just the tach reading dropped off ). We have had several technicians look and test for us, PDQ and Total Power. The consensus was a problem with the lengths of the wiring harnesses and or the resistors in the line. It has never shown up under a load. Now that we know the engines are running pretty close, we just make final adjustment to sinc them by ear and enjoy the ride.

Jimmy and Jonathan
Mr Busy Mv 34-059