9.9hp merc 4stroke tach pulses
 

I have a 1996 Merc 4 stroke that I want to get
an rpm reading on for the purpose of setting up/choosing
a prop. I have hooked a frequency meter up to
the tach signal. I also looked at it on my oscilloscope
to verify that the meter wasn't getting fooled. Seems to
be giving me a nice ~ square wave.

Now I have found some info on the motor that indicates
that it has 6 poles on the stator. Does this mean I get
six pulses per rev? or three?

I am getting just about 260 Hz at wot but about 95Hz at idle.


I am a bit confused as the motor should top out at about 5500rpm.

The 260Hz seems about right for 5200 rpm for 3 pulses. But
the 95 Hz seems to give me the right idle rpm (~950 rpm) for 6 pulses.


Any help?


Thanks


--

Almus Kenter
(617)495-7056


`` Pluralitas est ponenda sine neccesitate''
`` carpe per diem ''

Lloyd Sumpter wrote:
: On Mon, 29 Nov 2004 08:29:32 -0400, Almus Kenter wrote:

:
:
: I have a 1996 Merc 4 stroke that I want to get
: an rpm reading on for the purpose of setting up/choosing
: a prop.

: Please let me know what prop you end up with. I have a 2005 Merc 9.9
: 4-stroke and I think the prop is too steep (among other things!)

: Lloyd Sumpter
: "The Tin Boat" Mirrocraft 12



Right now I have a 9x9. The boat is a flat bottom skiff that
I built using stitch-n-glue. I think that 9x9 is over propped. I think they
make a 9x8 and a 9.? x 7.5.

Originally the boat had a high-thrust prop when it was used as a kicker.


--

Almus Kenter
(617)495-7056


`` Pluralitas est ponenda sine neccesitate''
`` carpe per diem ''

On Mon, 29 Nov 2004 08:29:32 -0400, Almus Kenter wrote:



I have a 1996 Merc 4 stroke that I want to get
an rpm reading on for the purpose of setting up/choosing
a prop.

Please let me know what prop you end up with. I have a 2005 Merc 9.9
4-stroke and I think the prop is too steep (among other things!)

Lloyd Sumpter
"The Tin Boat" Mirrocraft 12

"Almus Kenter" wrote in message
...


I have a 1996 Merc 4 stroke that I want to get
an rpm reading on for the purpose of setting up/choosing
a prop. I have hooked a frequency meter up to
the tach signal. I also looked at it on my oscilloscope
to verify that the meter wasn't getting fooled. Seems to
be giving me a nice ~ square wave.

Now I have found some info on the motor that indicates
that it has 6 poles on the stator. Does this mean I get
six pulses per rev? or three?

I am getting just about 260 Hz at wot but about 95Hz at idle.


I am a bit confused as the motor should top out at about 5500rpm.

The 260Hz seems about right for 5200 rpm for 3 pulses. But
the 95 Hz seems to give me the right idle rpm (~950 rpm) for 6 pulses.


Any help?


Thanks


--

Almus Kenter
(617)495-7056


`` Pluralitas est ponenda sine neccesitate''
`` carpe per diem ''


Just put a wrap of wire around a plug wire for an inductive pickup and hook
the o'scope to the wire. Double the number of pulses and that is your RPM.