Old Craftsman Mower Slows Down Then Stops

[Shawn R.]

This is an old mower but it still runs. I was actually trying to figure out what causes it to slow down and then stop after running for about 15 minutes. When it stops, I have to shut it off and let it rest for about 20 minutes and then it'll go again. The model number is: RZ125H42B and serial: 072401D001075. I believe it's somewhere around a 2001 model (correct me if I'm wrong). It has a Briggs & Stratton engine with 12.5HP. Motor model number: 289707. I bought it from a guy 3 years ago and when I first bought it, it ran just fine and did not slow down and stop like it's doing now. I guess I've had this issue for quite some time. I asked a mechanic if he knew anything about riding mowers, and he said a little. I told him about the problem I was having, and he said it could either be the spark plug or the carburetor.

I also called a shop that sells Zero Turns and asked them but they couldn't give me a straight answer. And I also asked several other people, but they've never heard of such a problem before. I figured the best place to start would have to be the spark plug and carburetor. So, I ordered a kit off of eBay that contained the spark plug, air filter, and carburetor. I changed the spark plug and air filter myself and had my cousin help me with the carburetor. It cranked up just fine but unfortunately, it did not fix the issue. There was no change in the time it took it to slow down and stop. I'm guessing the issue lies within the motor or the transmission but what do I know. I honestly don't know jack about riding mowers and that's why I'm asking you guys. Do you have any idea what the problem could be?

 

[bertsmobile1]

So what exactly is happening?
the drive slows down & stops ?
or the engine slows down & stops ?
If it is the engine dose it just slowly die or does it dire like it is running out of fuel or like you turned it off .

Being that it is a very old side valve ( L head ) my first place to check would be the valves
Side valve engines erode under the valve and eventually the exhaust valve does not fully close so the engine looses power, runs slower with less power, spins faster when cranking to start and the muffler will usually end up glowing red hot .
As the engine heats up and metal parts expand this gets worse
Checking the valves can be easy but expansive or difficult but cheap
Easy way is to remove the blower housing then remove the head
Rotate the engine at least 2 full revolutions and check that both valves close fully
This will cost you a new head gasket

The hard but cheap method is to remove the carburettor then remove the valve chest cover plate behind the carburettor and check the valve lash
On side valves it reduces over time so the valves can not fully close

If you have access to a compressor you can remove the spark plug put a stick down he plug hole then turn the engine to top dead center ( Piston closest to the spark plug ) then about 1/4" down
Cut a hole in a cork for an air duster shove it in the plug hole and blow compresses air into the cylinder while holding the flywheel so it can not move
If you hear air coming out of either the muffle or carburettor rotate the engine another full turn & repeat
If air is still coming out of the muffler then the exhaust valve needs to be adjusted

To adjust the valves you ned to remove metal from the end of the stem which is require the valve chest to be open and best done with the head off
I use a fine oil stone to remove material off the end of the vale stem, it is a slow job, remove check then remove more & check, repeat, repeat , repeat , till you get to the maximum gap which will reduce when you put the spring back one
The seat usually needs a touch up with some lapping paste

Sounds a lot more complicated than it is
Back in the early 1900 corn farmers who had never been to primary school would do this in their fields

And find a better mechanic

 

[StarTech]

Yes the mower was assembled on July 24, 2001.

This unti has a HG hydrostatic motion drive so as Bert note we need to narrow the failure description.

 

[Shawn R.]

So what exactly is happening?
the drive slows down & stops ?
or the engine slows down & stops ?
If it is the engine dose it just slowly die or does it dire like it is running out of fuel or like you turned it off .

Being that it is a very old side valve ( L head ) my first place to check would be the valves
Side valve engines erode under the valve and eventually the exhaust valve does not fully close so the engine looses power, runs slower with less power, spins faster when cranking to start and the muffler will usually end up glowing red hot .
As the engine heats up and metal parts expand this gets worse
Checking the valves can be easy but expansive or difficult but cheap
Easy way is to remove the blower housing then remove the head
Rotate the engine at least 2 full revolutions and check that both valves close fully
This will cost you a new head gasket

The hard but cheap method is to remove the carburettor then remove the valve chest cover plate behind the carburettor and check the valve lash
On side valves it reduces over time so the valves can not fully close

If you have access to a compressor you can remove the spark plug put a stick down he plug hole then turn the engine to top dead center ( Piston closest to the spark plug ) then about 1/4" down
Cut a hole in a cork for an air duster shove it in the plug hole and blow compresses air into the cylinder while holding the flywheel so it can not move
If you hear air coming out of either the muffle or carburettor rotate the engine another full turn & repeat
If air is still coming out of the muffler then the exhaust valve needs to be adjusted

To adjust the valves you ned to remove metal from the end of the stem which is require the valve chest to be open and best done with the head off
I use a fine oil stone to remove material off the end of the vale stem, it is a slow job, remove check then remove more & check, repeat, repeat , repeat , till you get to the maximum gap which will reduce when you put the spring back one
The seat usually needs a touch up with some lapping paste

Sounds a lot more complicated than it is
Back in the early 1900 corn farmers who had never been to primary school would do this in their fields

And find a better mechanic

The drive slows down and stops. The engine runs fast the whole time.

 

[bertsmobile1]

Excellent so now we know it is a transmission problem , either the belt or the transmission
Considering the age of the unit the hydro could be plain worn out they have a finite life
Remove it drain the oil and replace it with nice fresh 20w50 full synthetic
The symptoms you have are those of a worn out unit where as the oil gets hot it bypasses the motor so no drive
Usually it will groan quite loud and it gets louder as the oil gets hotter .

Before you do that check the transmission belt and the pulleys
Check the engine pulley for polish in the bottom of the V groove indicating that it is worn out
Check the idlers for worn spots, smooth & quiet running
Check the pivot point for the plate the tension pulley is on , it will probably be flogged out oval
And of course the belt itself, they wear thin on the sides so run deeper in the pulleys so become loose & slip .

Take photos before you take anything off so you know where it goes back and in particular the springs
My cheap & nasty test of the drive is to remove the deck , brake off, grab each side of the belt and push - pull on it.
If the system is good you should be able to turn the engine over using the transmission belt
If it slips then some thing needs replacing .

 

[Augger]

Excellent so now we know it is a transmission problem , either the belt or the transmission
Considering the age of the unit the hydro could be plain worn out they have a finite life
Remove it drain the oil and replace it with nice fresh 20w50 full synthetic
The symptoms you have are those of a worn out unit where as the oil gets hot it bypasses the motor so no drive
Usually it will groan quite loud and it gets louder as the oil gets hotter .

Before you do that check the transmission belt and the pulleys
Check the engine pulley for polish in the bottom of the V groove indicating that it is worn out
Check the idlers for worn spots, smooth & quiet running
Check the pivot point for the plate the tension pulley is on , it will probably be flogged out oval
And of course the belt itself, they wear thin on the sides so run deeper in the pulleys so become loose & slip .

Take photos before you take anything off so you know where it goes back and in particular the springs
My cheap & nasty test of the drive is to remove the deck , brake off, grab each side of the belt and push - pull on it.
If the system is good you should be able to turn the engine over using the transmission belt
If it slips then some thing needs replacing .

Does it have a rear motor and rear drive? I just replaced the clutch in the drive and then it was good. I made a few extra clutch packs if you need a kit? Email me and I can send you some pictures. aug_ger@hotmail.com