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Lawn Boy runs high rpm

Jun 4, 2013#1

M

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.

Jun 4, 2013#2

impalass

Mary Wilson said:
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.

\

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

Jun 4, 2013#3

impalass

Could you mention which model number you have.

Jun 4, 2013#4

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.

Jun 4, 2013#5

M

Mary Wilson

Two-Stroke said:
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.

Jun 4, 2013#6

impalass

Mary Wilson said:
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.

Jun 4, 2013#7

M

Mary Wilson

impalass said:
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.

Jun 4, 2013#8

impalass

Mary Wilson said:
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.

Jun 5, 2013#9

WhyZed

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

Jun 5, 2013#10

M

Mary Wilson

WhyZed said:
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.

Jun 5, 2013#11

impalass

When you had the carb off did you the reeds. With both carbs you have the same symptoms. Are the filters clean, you might two, one in the gas tank and the other in the carb. Depending on which carb you have one is in the inlet supply which is a small wire mesh tube and the other in the carb over the main jet.
When you cleaned the carb did you take out the main jet and checked the holes were clear. You have a very small hole near the top of the main jet.

Jun 5, 2013#12

M

Mary Wilson

impalass said:
When you had the carb off did you the reeds. With both carbs you have the same symptoms. Are the filters clean, you might two, one in the gas tank and the other in the carb. Depending on which carb you have one is in the inlet supply which is a small wire mesh tube and the other in the carb over the main jet.
When you cleaned the carb did you take out the main jet and checked the holes were clear. You have a very small hole near the top of the main jet.

The filter in the carb looked beat up so I just removed it. I blew through the line to the tank and it didn't seem stopped up. It's very possible I didn't get the carb as clean as I could have. I'll probably take it apart again because I put it back together with some of the old parts that I meant to replace but I didn't have them at the time. I'll do a re-cleaning in a day or two. I'll probably check and see if maybe I created an air leak when I took all the stuff off the engine. Maybe a bolt hole letting air in?

Jun 5, 2013#13

Two-Stroke

I don't think running too lean will cause the symptoms you describe. The governor should still cut in and close the throttle at the same rpm. A photo of the carb (governor area) would help. I believe the governor is the problem.

An in-line fuel filter (made for 1/4" fuel line -- a generic item -- not expensive) is a good thing to install even if you didn't remove the stock fuel filter.

A good fuel filter will prevent a lot of the problems that you read about on this forum. :thumbsup:

Jun 6, 2013#14

M

Mary Wilson

Two-Stroke said:
I don't think running too lean will cause the symptoms you describe. The governor should still cut in and close the throttle at the same rpm. A photo of the carb (governor area) would help. I believe the governor is the problem.

An in-line fuel filter (made for 1/4" fuel line -- a generic item -- not expensive) is a good thing to install even if you didn't remove the stock fuel filter.

A good fuel filter will prevent a lot of the problems that you read about on this forum. :thumbsup:

Could be, but I did find something which may or may not be a problem. I took it apart today again and took the carb apart and soaked it in carb cleaner. The carb looked pretty clean but could still be plugged somewhere inside, I guess. What I noticed is a hole. I stuck a wire in it and it went in pretty far (at least an inch) before it touched something. I don't know if it's a blind hole or an open ended one, I couldn't see into the hole because some other stuff was in the way, so I put a bolt in the hole anyway with some sealer around it. I'll let you know later if that's it or not. I've worked on a few hundred chain saws and I can tell you that a lean engine will turn more rpms for the same throttle opening, it's like having a second throttle only without any fuel. If the hole is too big, of course the engine won't run at all, but with a little hole it will run too lean which will kill a 2 stroke. As for the fuel filter, I probably have one. I usually buy them at flea markets.
I really like this little mower, weights very little, has a magnesium deck. I've been using it sparingly to mow a bank in front of the house, it kinda wears me out to use my other, heavier mower.

Jun 6, 2013#15

impalass

Mary Wilson said:
Could be, but I did find something which may or may not be a problem. I took it apart today again and took the carb apart and soaked it in carb cleaner. The carb looked pretty clean but could still be plugged somewhere inside, I guess. What I noticed is a hole. I stuck a wire in it and it went in pretty far (at least an inch) before it touched something. I don't know if it's a blind hole or an open ended one, I couldn't see into the hole because some other stuff was in the way, so I put a bolt in the hole anyway with some sealer around it. I'll let you know later if that's it or not. I've worked on a few hundred chain saws and I can tell you that a lean engine will turn more rpms for the same throttle opening, it's like having a second throttle only without any fuel. If the hole is too big, of course the engine won't run at all, but with a little hole it will run too lean which will kill a 2 stroke. As for the fuel filter, I probably have one. I usually buy them at flea markets.
I really like this little mower, weights very little, has a magnesium deck. I've been using it sparingly to mow a bank in front of the house, it kinda wears me out to use my other, heavier mower.

That could be a air vent hole. If that is a plastic carb you do soak it in a cab cleaner. Did you read the manual that i gave you a link to.

Jun 7, 2013#16

impalass

Mary Wilson said:
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.

https://lookup3.toro.com/Ill/1x/5/5707/80290005.gif

Jun 8, 2013#17

M

Mary Wilson

Mary Wilson said:
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.

I tried again today (Saturday) and it did the same thing. I took it apart again last week and cleaned the carb out thoroughly this time and blew it out with compressed air. New air filter, no leaks anywhere. The saw ran at low rpm for awhile, then as I was mowing the mower touched against a small tree and the motor sped up. I shut it off and tried starting it and was hard to start so I primed it and it started but ran fast. I then primed it some more and it slowed down but only momentarily. The thing just seems to me it's not getting enough fuel. I'm wondering now if the float might be sticking shut. I'm going to try to find a kit for it and see if it helps...kinda running out of ideas.

Jun 8, 2013#18

WhyZed

Hey Mary Wilson's Husband

I uploaded a 5 minute video and linked it to this post;
http://www.lawnmowerforum.com/lawn-...ommercial-6277-bricktop-1969-1970-1971-a.html
The problem you are having and the solution might be explained near the end of it.

Check it, hope that is the problem/solution..

Zed

Jun 8, 2013#19

M

Mary Wilson

WhyZed said:
Hey Mary Wilson's Husband

I uploaded a 5 minute video and linked it to this post;
http://www.lawnmowerforum.com/lawn-...ommercial-6277-bricktop-1969-1970-1971-a.html
The problem you are having and the solution might be explained near the end of it.

Check it, hope that is the problem/solution..

Zed

I watched your video and I can tell you that my problem is nothing like that. Mine appears to be a lean condition but I can't tell from what. As of today I've changed both crank seals, changed the carburetor from a LB that was running fine, checked the block for leaks visually only (maybe I need to rig up a crank pressure tester) and still the engine runs wide open. I looked at the carb while it was running and the governor has the carb butterfly closed. I'm almost to the point of buying another mower and using this one for parts.

Jun 8, 2013#20

WhyZed

Mary Wilson said:
I watched your video and I can tell you that my problem is nothing like that. Mine appears to be a lean condition but I can't tell from what. As of today I've changed both crank seals, changed the carburetor from a LB that was running fine, checked the block for leaks visually only (maybe I need to rig up a crank pressure tester) and still the engine runs wide open. I looked at the carb while it was running and the governor has the carb butterfly closed. I'm almost to the point of buying another mower and using this one for parts.

Ok, I was hoping that was the problem.

Have you checked or changed the gasket between the carb and the reeds? (Sorry I didn't re-read the entire thread).
Other then that, I would agree, a leakdown test to find the air leak.

Jun 8, 2013#21

Two-Stroke

Mary Wilson said:
I watched your video and I can tell you that my problem is nothing like that. Mine appears to be a lean condition but I can't tell from what. As of today I've changed both crank seals, changed the carburetor from a LB that was running fine, checked the block for leaks visually only (maybe I need to rig up a crank pressure tester) and still the engine runs wide open. I looked at the carb while it was running and the governor has the carb butterfly closed. I'm almost to the point of buying another mower and using this one for parts.

I think there must be a fairly significant leak for it to run fast with the butterfly closed. Keep in mind that, unlike a chainsaw, a rotary mower has a fair amount of drag (even without any grass underneath) due to the power necessary to turn the blade -- it's like a propeller.

The fact that it does this with another carb (that you know is good) is a real puzzler.

You are sure that the butterfly is closed when it's revving high -- correct? That's the most baffling part. :confused2:

Jun 8, 2013#22

WhyZed

Ya, baffling :confused2:

The confusing thing for me is, "it was running fine, rubbed a small tree then it started doing it again".
That is key but what it unlocks is ??? :confused2:

Jun 8, 2013#23

M

Mary Wilson

WhyZed said:
Ya, baffling :confused2:

The confusing thing for me is, "it was running fine, rubbed a small tree then it started doing it again".
That is key but what it unlocks is ??? :confused2:

I should have used the word "tapped". I didn't hit it very hard, just bumped into it. I thought maybe it stuck the float but I changed carburetors and it does the same thing. This week I'm going to try to fix up something to check the engine crankcase pressure, like they do on chainsaws, just haven't got it done yet.

Jun 8, 2013#24

M

Mary Wilson

Two-Stroke said:
I think there must be a fairly significant leak for it to run fast with the butterfly closed. Keep in mind that, unlike a chainsaw, a rotary mower has a fair amount of drag (even without any grass underneath) due to the power necessary to turn the blade -- it's like a propeller.

The fact that it does this with another carb (that you know is good) is a real puzzler.

You are sure that the butterfly is closed when it's revving high -- correct? That's the most baffling part. :confused2:

The butterfly has a hole in it set for a fast idle, I suppose. I figured that plus the air leak, if that's what it is, might be enough to make it speed. I don't think the problem is in the tank because when you open the valve with the fuel line disconnected fuel pours out. The gas cap has a good vent also.
When the mower is in fairly tall grass I can kinda control the rpms but it's when the grass is light or short that it runs away with itself.
I might add that when I changed the carbs I didn't do any adjustment to the good running one, just unbolted one and replaced it with another so I wouldn't have the confusion of whether I set it right or not.

Jun 8, 2013#25

impalass

Mary Wilson said:
The butterfly has a hole in it set for a fast idle, I suppose. I figured that plus the air leak, if that's what it is, might be enough to make it speed. I don't think the problem is in the tank because when you open the valve with the fuel line disconnected fuel pours out. The gas cap has a good vent also.
When the mower is in fairly tall grass I can kinda control the rpms but it's when the grass is light or short that it runs away with itself.
I might add that when I changed the carbs I didn't do any adjustment to the good running one, just unbolted one and replaced it with another so I wouldn't have the confusion of whether I set it right or not.

Did you check to see if the bolts are tight on the bottom end cap.

Jun 8, 2013#26

M

Mary Wilson

impalass said:
Did you check to see if the bolts are tight on the bottom end cap.

No, I haven't done that. I guess I should check all the engine bolts...I just assumed they were okay since they haven't been messed with. I'll try that next.

Jun 9, 2013#27

B

bwright1818

This is a great thread. I also have an F engine which seems to have the exact same problem, although I have done little to solve it yet, other than a carb cleaning. (I currently own 13 Lawnboys, 10 chain saws and am a boat mechanic by trade; so I have done a few carbs.)

I wonder: When you say the carb is "closed," it's sort of relative as you know, because it doen't take much throttle opening to rev high with no load. Can you take some sort of a hooked tool to actually pull the vane dead closed while it's running? If it STILL revs, boy would you have an air leak then!

Can't wait to hear how this one tuns out!

Jun 9, 2013#28

M

Mary Wilson

bwright1818 said:
This is a great thread. I also have an F engine which seems to have the exact same problem, although I have done little to solve it yet, other than a carb cleaning. (I currently own 13 Lawnboys, 10 chain saws and am a boat mechanic by trade; so I have done a few carbs.)

I wonder: When you say the carb is "closed," it's sort of relative as you know, because it doen't take much throttle opening to rev high with no load. Can you take some sort of a hooked tool to actually pull the vane dead closed while it's running? If it STILL revs, boy would you have an air leak then!

Can't wait to hear how this one tuns out!

Me too, except I'll probably be glad when it's actually fixed! I'll let you guys know what I find (if I find it). I'm pretty determined on this one so I'll probably come up with something. Joe

Jun 9, 2013#29

M

Mary Wilson

bwright1818 said:
This is a great thread. I also have an F engine which seems to have the exact same problem, although I have done little to solve it yet, other than a carb cleaning. (I currently own 13 Lawnboys, 10 chain saws and am a boat mechanic by trade; so I have done a few carbs.)

I wonder: When you say the carb is "closed," it's sort of relative as you know, because it doen't take much throttle opening to rev high with no load. Can you take some sort of a hooked tool to actually pull the vane dead closed while it's running? If it STILL revs, boy would you have an air leak then!

Can't wait to hear how this one tuns out!

I'm proud to announce the mower is fixed! The problem was an air leak at the base of the carburetor caused by the pulse hole leaking there. My last stab at fixing it involved plugging up the hole with RTV and making a new, thicker gasket for the carb with the hole deleted. I started it up a few minutes ago and it ran normally, actually a bit slow, so I may have to adjust the governor a notch or two. It's set on the fastest of the two settings and is just a little slow. It two cycles in the taller grass like it's supposed to so maybe now all I need to do is adjust. Thanks for the input. Joe

Jun 9, 2013#30

B

bwright1818

Hmmm, I ALMOST took mine out of service for a new deck, today. I drained the gas out today, so I could bring it in the cellar. Maybe I should have a look at my gasket, too. I have had this machine for 16 years and have put many, many, MANY hours on it. And I got it, used! I thought it was done. It would be unbelievable if all it needs is a gasket! But my machine has pretty much EXACTLY the same symptoms....

Good job on yours! Persistance pays!

Jun 9, 2013#31

M

Mary Wilson

bwright1818 said:
Hmmm, I ALMOST took mine out of service for a new deck, today. I drained the gas out today, so I could bring it in the cellar. Maybe I should have a look at my gasket, too. I have had this machine for 16 years and have put many, many, MANY hours on it. And I got it, used! I thought it was done. It would be unbelievable if all it needs is a gasket! But my machine has pretty much EXACTLY the same symptoms....

Good job on yours! Persistance pays!

Thanks! If yours has a plastic carburetor it sure would be worth a look. The metal ones pretty well cover up that hole but guess it wouldn't hurt to look at it also. I made a gasket out of a thick piece of cardboard and covered it with rtv.

Jun 10, 2013#32

impalass

Mary Wilson said:
I'm proud to announce the mower is fixed! The problem was an air leak at the base of the carburetor caused by the pulse hole leaking there. My last stab at fixing it involved plugging up the hole with RTV and making a new, thicker gasket for the carb with the hole deleted. I started it up a few minutes ago and it ran normally, actually a bit slow, so I may have to adjust the governor a notch or two. It's set on the fastest of the two settings and is just a little slow. It two cycles in the taller grass like it's supposed to so maybe now all I need to do is adjust. Thanks for the input. Joe

The only hole i see is a small hole above the main venturi which matches the hole in the end cap and my gasket has a small hole. Tell me which hole you plugged in the picture that i posted.

Aug 7, 2013#33

M

Mary Wilson

impalass said:
The only hole i see is a small hole above the main venturi which matches the hole in the end cap and my gasket has a small hole. Tell me which hole you plugged in the picture that i posted.

That's a different carb than mine. I plugged up the hole you are referring to since it's not used on that type machine. I think I read it's used on snow blowers. Anyway, my main problem was a leak at the carb flange so I just made sure it didn't leak any more. Sorry about the late reply..

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Lawn Boy runs high rpm

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