Lawn Boy runs high rpm

[Mary Wilson]

I have a Lawn Boy mower with the F engine that has been my nemesis this last two years. After the engine warms up for a few minutes it's like you opened a chainsaw engine wide open and held it there. We've tried cleaning the carb, blowing out the fuel lines and even installed a bottom crank seal. Still, it runs slow at first then wide open. The carb vein appears to be free. Any help would be appreciated.

 

[impalass]

I have a Lawn Boy mower with the F engine that has been my nemesis this last two years. After the engine warms up for a few minutes it's like you opened a chainsaw engine wide open and held it there. We've tried cleaning the carb, blowing out the fuel lines and even installed a bottom crank seal. Still, it runs slow at first then wide open. The carb vein appears to be free. Any help would be appreciated.

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Check the spring that governs the vane that is where you have the problem. If you run it at high speed you will break the connecting rod.
Here is a link to the engine manual.

http://www.scribd.com/doc/26622228/Lawn-Boy-Service-Manual-1950-88-Complete

https://lookup3.toro.com/ttcGateway/acrobat/manuals/lball.html

 

[impalass]

Could you mention which model number you have.

 

[Two-Stroke]

If the suggestion in post #2 doesn't work could you take off the shroud (the big plastic cover containing the gas tank) and take a photo of the carb. The governor is not working and it's either sticking or some part is not connected properly.

Actually, before you take off the shroud, check that the governor mechanism can move freely.

:welcome:

You've got a good mower. Don't get discouraged.

 

[Mary Wilson]

If the suggestion in post #2 doesn't work could you take off the shroud (the big plastic cover containing the gas tank) and take a photo of the carb. The governor is not working and it's either sticking or some part is not connected properly.

Actually, before you take off the shroud, check that the governor mechanism can move freely.

:welcome:

You've got a good mower. Don't get discouraged.

We've done all that, don't know the model number but it does have the plastic carburetor. The vane does spring back and seems to work free in the housing. I wonder if it would be a good idea to take the air filter off and look at the carb to see if the butterfly is staying open or maybe there's an air leak? I tried turning the vane adjustment knob but it won't click like my other one does, it has the little handle for slow or fast which is on slow but doesn't seem to affect it.

 

[impalass]

We've done all that, don't know the model number but it does have the plastic carburetor. The vane does spring back and seems to work free in the housing. I wonder if it would be a good idea to take the air filter off and look at the carb to see if the butterfly is staying open or maybe there's an air leak? I tried turning the vane adjustment knob but it won't click like my other one does, it has the little handle for slow or fast which is on slow but doesn't seem to affect it.

When you move the little handle from low to high the RPM should increase, if not you have a problem with the spring under the vane. Do you have a hex or round knob. The model number is usually on a small plate at the rear of the mower between the wheels.

 

[Mary Wilson]

When you move the little handle from low to high the RPM should increase, if not you have a problem with the spring under the vane. Do you have a hex or round knob. The model number is usually on a small plate at the rear of the mower between the wheels.

I think the engine has been changed so I don't think you can go by the model number on the deck. It has the hexagon knob and doesn't appear to want to turn. You can change the rpm by moving the handle but within a few minutes it over revs and the only thing you can do is shut it off.

 

[impalass]

I think the engine has been changed so I don't think you can go by the model number on the deck. It has the hexagon knob and doesn't appear to want to turn. You can change the rpm by moving the handle but within a few minutes it over revs and the only thing you can do is shut it off.

Part number for the spring with the hex collar is 609638 and it cost about 10 dollars and is very easy to change. You could try that.

 

[WhyZed]

Can you get us a picture or two Mary Wilson?
It will help us help you.

 

[Mary Wilson]

Can you get us a picture or two Mary Wilson?
It will help us help you.

I had to use my wife's name to log on. Something wrong with my password or something. Tried opening a new account but it wouldn't work either so I used my wife's name and password. Joe

I'll try to get a few pics up, maybe later today. I did look while the engine was running and the air vane was going back and forth so it's not stuck and the spring appears to be working. I think my problem is the engine is running way too lean, either has an air leak or not getting enough gas. I've had several Lawn Boys over the years and most have done well for me. I bought this mower strictly for the deck and put another engine on it. The one I put on originally came with an electric start and bagger, self propelled, and I didn't use any of that stuff. I had to change the carburetor and top cover. I tried to make it like my Lawn Boy Utility except with an alloy deck. I tried a Walbro carb with choke instead of the primer and the engine ran exactly like it does now. Should I bother trying to change the upper crank seal? The number on the deck is S19ZPN.