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Correct speed for rotary lawnmower engine?

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Correct speed for rotary lawnmower engine? Jeff Wisnia 05-09-2007
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Posted by Jeff Wisnia on May 9, 2007, 1:30 pm

I've got a 21" Toro self propelled rotary mower with a 3.75 hp Briggs
engine on it.

Whe I used it today for the first time this season I had a feeling the
engine might be running a little slower than it had in the past, as I
seemed to be walking "less fast" to keep up with it.

I measured the RPMs with my non-contact tach and the engines's "full
speed" with no load was 3,000 RPMs, and it didn't sound like it dropped
off significantly under load.

My memory is telling me governed full speed for that kind of setup
should be more like 3,500 RPM. Can someone confirm that?

The governor seems to be doing it's job, but I've got a feeling it's
spring has stretched a bit over the years. The engine speed will
increase fine if I "assist" the spring with my fingertips, so I can
probably tweak the speed up by rebending the throttle lever end of the
spring to make it a bit shorter, (or by buying a new spring). The other
end of the spring is as far away from the throttle lever as the speed
control lever can go.

Thanks guys,

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.



Posted by Sev on May 9, 2007, 1:44 pm
> I've got a 21" Toro self propelled rotary mower with a 3.75 hp Briggs
> engine on it.
>
> Whe I used it today for the first time this season I had a feeling the
> engine might be running a little slower than it had in the past, as I
> seemed to be walking "less fast" to keep up with it.
>
> I measured the RPMs with my non-contact tach and the engines's "full
> speed" with no load was 3,000 RPMs, and it didn't sound like it dropped
> off significantly under load.
>
> My memory is telling me governed full speed for that kind of setup
> should be more like 3,500 RPM. Can someone confirm that?
>
> The governor seems to be doing it's job, but I've got a feeling it's
> spring has stretched a bit over the years. The engine speed will
> increase fine if I "assist" the spring with my fingertips, so I can
> probably tweak the speed up by rebending the throttle lever end of the
> spring to make it a bit shorter, (or by buying a new spring). The other
> end of the spring is as far away from the throttle lever as the speed
> control lever can go.
>
> Thanks guys,
>
> Jeff
> --
> Jeffry Wisnia
> (W1BSV + Brass Rat '57 EE)
> The speed of light is 1.8*10^12 furlongs per fortnight.

Perhaps this is a feature where the aging of the machine matches aging
of the operator? But apparently you're not ready for that yet... All
I know is these 1- speed engines are designed to run at their set
speed, they warn against tampering, so check the specs before any
sdjustments.


Posted by on May 9, 2007, 3:45 pm
On May 9, 1:30 pm, Jeff W3
> --
> Jeffry Wisnia
> (W1BSV + Brass Rat '57 EE)
> The speed of light is 1.8*10^12 furlongs per fortnight.

Also of interest is speed/longevity. These engines are not pressure-
lubed at main/rod journals. So ... I'll wager that your longevity
at 3K rpm will be much greater than at 3.5K.

HTH,
J


Posted by Meat Plow on May 9, 2007, 7:43 pm
On Wed, 09 May 2007 13:30:20 -0400, Jeff Wisnia wrote:

>
> I've got a 21" Toro self propelled rotary mower with a 3.75 hp Briggs
> engine on it.
>
> Whe I used it today for the first time this season I had a feeling the
> engine might be running a little slower than it had in the past, as I
> seemed to be walking "less fast" to keep up with it.
>
> I measured the RPMs with my non-contact tach and the engines's "full
> speed" with no load was 3,000 RPMs, and it didn't sound like it dropped
> off significantly under load.
>
> My memory is telling me governed full speed for that kind of setup
> should be more like 3,500 RPM. Can someone confirm that?
>
> The governor seems to be doing it's job, but I've got a feeling it's
> spring has stretched a bit over the years. The engine speed will
> increase fine if I "assist" the spring with my fingertips, so I can
> probably tweak the speed up by rebending the throttle lever end of the
> spring to make it a bit shorter, (or by buying a new spring). The other
> end of the spring is as far away from the throttle lever as the speed
> control lever can go.
>
> Thanks guys,
>

Make sure the governor vane arm and the butterfly moves freely. That motor
should red line at 4K so don't push the envelope. Buy a new spring, lube
everything, make sure it has 100% new gas, oil, air filter then mow your
lawn.

--
#1 Offishul Ruiner of Usenet, March 2007
#1 Usenet Asshole, March 2007
#1 Bartlo Pset, March 13-24 2007
#10 Most hated Usenetizen of all time
Pierre Salinger Memorial Hook, Line & Sinker, June 2004
COOSN-266-06-25794



Posted by Bob M. on May 9, 2007, 9:40 pm

>
> I've got a 21" Toro self propelled rotary mower with a 3.75 hp Briggs
> engine on it.
>
> Whe I used it today for the first time this season I had a feeling the
> engine might be running a little slower than it had in the past, as I
> seemed to be walking "less fast" to keep up with it

Most newer mowers don't even have a throttle control - they run full-tilt
all the time. Mine does anyhow. They do this partly to save money but also
because the control just isn't needed.


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