changed prop and didnt change RPM???
 

hi,
i was having trouble getting WOT on my 20' Reinell merc. 165.
i was running a 19 pitch and could only obtain 3500 RPM. i picked up a 17 from my local dealer to try out and i still have the same RPM. i am confused as to why the RPM didnt change with the prop change. i was expecting it to pick up to 4100 or so.
i was hoping that someone here might have an idea.
some other specs: 8' @ idle, 30' @ 3000RPM. new filters, gas, plugs, wires, cap, rotor, spark arrestor clean, outdrive rebuilt by merc tech. i am at a loss.
tia
brian

Re: changed prop and didnt change RPM???
 

general rule of thumb 1 in in pitch = 200 rpms

Re: changed prop and didnt change RPM???
 

GOODT, thanks for the post. i was expecting about 400-500 but it didnt change at all.
brian

Re: changed prop and didnt change RPM???
 

what is the diameter of the new...of the old.... ???

Re: changed prop and didnt change RPM???
 

both are 14.5" both are aluminum.

Re: changed prop and didnt change RPM???
 

Make sure the tach is right,what speeds are you seeing?

Re: changed prop and didnt change RPM???
 

i have a tach hooked up to the motor as well and both are indicating the same.
i am showing an average of 28MPH (GPS) with both props.

Re: changed prop and didnt change RPM???
 

I don't think the props are the problem,you are down on power it seems to me.How many hrs on it? merc heads are known for tuliping valves,making rpm a loss,also could be valve springs,that will cause rpm loss.

Re: changed prop and didnt change RPM???
 

i just had the head off and all was good. had the valves resurfaced and new seals. i was out again tonight and still the same thing. both tachs indicating 3600. does anyone know what i should be running for total timing on a 165 merc? i have about 30', but i was told that in a car that motor should be about 36 total. would that be the same in a boat? thanks again
brian