Correct speed for rotary lawnmower engine?

[Jeff Wisnia]

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

[Sev]

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.

[barry]

On May 9, 1:30 pm, Jeff W3

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

[Meat Plow]

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.

[Bob M.]

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.

[Steve Barker]

3,600 is typical for these engines. They will tolerate more however. We set most of ours to 4,000 - 4,100

[Steve Barker]

They don't run "full tilt". They are still governed at 3600 even without a throttle control.

[Edwin Pawlowski]

Are you sure the self propelling drive is not slipping?

[Jeff Wisnia]

I doubt that Ed, there's only one belt between the engine shaft and the worm gear reduction box on the front axle.

That belt is tighter than a bull's arse in fly season.

My Toro mower is about 30 year old now. It's original Tecumsah engine wore to the point where you could barely feel any compression when pulling it over, so I replaced it about six years ago with the present B&S which I ordered from Northern Tool.

I figger that if I'm faithfull to my tools and maintain them they'll respond in kind, and from what I can see, my old Toro mower is built a lot sturdier that the crap on sale now. Same goes for my Airen's Sno-Thro, "The widow maker"* which just completed its 42nd winter clearing our driveway.

Jeff

• So named by me because it's totally devoid of any of those "safety" features Airen's has been blackmailed into adding to their machines by legions of scumbag lawyers. (Just my .02)

[Jeff Wisnia]

Thanks Steve. I'll tweak it up to 3600 this weekend.

Jeff