Zero Turn won't reach full RPM and randomly accelerates to normal RPM

[Beemer Farm]

New to the forum and new to working on Kubotas. I did search the forum, but did not find much related to my mower...

I have a 2011 Z725 - 60" with a Kholer 25HP engine that usually starts and runs with what seems like about 1/3 throttle, though the throttle is at full. After a while, but very randomly, it accelerates to full RPM. it will then cycle every so often back and forth from that 1/3 RPM to full. Sometimes it will run for an hour at full RPM.

I have removed the belt and checked that each pulley turns freely and does not have significant play in the shaft bearings. I suspect there is a fuel delivery issue (or perhaps a linkage issue), of some type of electronic safety or cut off, but I'm quite confused because it doesn't stop the engine, it just goes to about 1/3 power. I doubt it is the inline filter, because occasionally it runs great. There is no obstruction in the mower deck. I have not investigated the tank other than to check that the manual fuel shutoff valve is fully open. I keep the tank quite full.

Thank you for any insight you may have.

 

[lynnmor]

I guess that you have a carburetor rather than fuel injection. I would start by insuring that the fuel tank is vented and not causing a vacuum. Next, I would clean out the carburetor, you might have debris randomly restricting fuel flow.

 

[JimmyJazz]

Also, check your air filter for excessive debris. Good luck.

 

[RCW]

I guess that you have a carburetor rather than fuel injection. I would start by insuring that the fuel tank is vented and not causing a vacuum. Next, I would clean out the carburetor, you might have debris randomly restricting fuel flow.

Following @lynnmor - - do you use ethanol gas? If so, could be some corrosion issues associated with e-gas.

 

[TheOldHokie]

New to the forum and new to working on Kubotas. I did search the forum, but did not find much related to my mower...

I have a 2011 Z725 - 60" with a Kholer 25HP engine that usually starts and runs with what seems like about 1/3 throttle, though the throttle is a full. After a while, but very randomly, it accelerates to full RPM. it will then cycle every so often back and forth from that 1/3 RPM to full. Sometimes it will run for an hour at full RPM.

I have removed the belt and checked that each pulley turns freely and does not have significant play in the shaft bearings. I suspect there is a fuel delivery issue (or perhaps a linkage issue), of some type of electronic safety of cut off, but I'm quite confused because it doesn't ever stop the engine, it just goes to about 1/3 power. I doubt it is the inline filter, because occasionally it runs great. There is no obstruction in the mower deck. I have not investigated the tank. I keep the tank quite full.

Thank you for any insight you may have.

I think I would be looking for the governor.

Dan

 

[lynnmor]

I think I would be looking for the governor.

Dan

That would be my next suggestion but I didn't want to mention that till other things are checked. Governors can be difficult without the proper instructions and we don't know the skill set of the OP.

 

[lugbolt]

replace the spark plugs lately? If not, try it. Kinda sounds like one is partially fouled.

Kohler? If the plugs are new (not cleaned...replace them), compression is good, valve clearance is correct, could possibly be a coil failing. Wouldn't surprise me, not with it being a Kohler.

 

[Beemer Farm]

Also, check your air filter for excessive debris. Good luck.

Air filters are clean and recently replaced.

 

[Beemer Farm]

I guess that you have a carburetor rather than fuel injection. I would start by insuring that the fuel tank is vented and not causing a vacuum. Next, I would clean out the carburetor, you might have debris randomly restricting fuel flow.

I will check that the cap is venting properly. Also will take a look at whether it has a carb or injection.

 

[Beemer Farm]

Following @lynnmor - - do you use ethanol gas? If so, could be some corrosion issues associated with e-gas.

No ethanol. I only use premium which is ethanol free in our area.

 

[Beemer Farm]

replace the spark plugs lately? If not, try it. Kinda sounds like one is partially fouled.

Kohler? If the plugs are new (not cleaned...replace them), compression is good, valve clearance is correct, could possibly be a coil failing. Wouldn't surprise me, not with it being a Kohler.

A coil failing is interesting, but I'm surprised that is runs so long at full RPM occasionally. I will look at a fresh coil as it should be both easy and worth doing for reliability

 

[Beemer Farm]

That would be my next suggestion but I didn't want to mention that till other things are checked. Governors can be difficult without the proper instructions and we don't know the skill set of the OP.

I agree that it very likely could be a governor issue. I checked for freedom of movement statically and with it running. I will need to find a maintenance manual to go beyond that, unless you can recommend a testing method...

 

[RCW]

No ethanol. I only use premium which is ethanol free in our area.

That’s great.

In our area Premium 93 Octane is still Ethanol Gas.

Ethanol Free is typically 91 Octane and labeled as Ethanol Free.

Lots of local folks don’t realize Premium (in our area) is still Ethanol Gas.

 

[TheOldHokie]

I agree that it very likely could be a governor issue. I checked for freedom of movement statically and with it running. I will need to find a maintenance manual to go beyond that, unless you can recommend a testing method...

Here is the Kohler service manual. The govermer is a simple fly weight linkage and you should be able to manually force it to full speed if thats the problem. If that does not yield success I would read the section on the high speed jet circuit in the carburetor.

https://resources.kohler.com/power/kohler/enginesUS/pdf/24_690_37_EN.pdf

Dan