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

 

[lugbolt]

The reason I didnt mention governor or it's adjustment is that Kohler is not known for governor problems. Briggs is, but not Kohler. Kohler is usually coils and/or head gaskets. Thus when I hear someone complain about "lack of power", I usually think of coil(s) first and then head gaskets, although head gaskets are usually obvious on Kohler engines. Noisy, smoke from places that smoke should be, etc.

I have a ZG127. I know, different mower, different engine. Went through this last year. Run fine most of the time, every so often it would run at half power half speed. One day it started to bog and I grabbed the LH spark plug wire and pulled it off, engine died and I got a good jolt. Started it back up, ran fine. Then it started to miss again, so I got off, pulled the RH plug wire off, no change-so I knew it was RH cylinder issue. Knowing what I do, I picked up a coil "retrofit kit" and swapped it. No problems since, starts better, uses a little less fuel, etc.

The early Z700 Kohlers had some issue with coils, as did a lot of the SV840 engines on the ZG100 series. They used digital spark advance ignition modules (DSAI) and they were quite well known for failures, so Kohler offers a kit that replaces the DSAI coils with MDI coils, which are your standard magnetic pickup style coils, that to my knowledge, have not had a single failure with. At the shop (dealer) we actually quit selling Kohler powered Z700 series because they were failure prone, and the people buying them were usually commercial customers who did not value downtime much. Sold a lot of the Kawasaki-powered units and later on the EFI units (Z781i) but kind of quit on the Kohler-powered Z700's.

 

[TheOldHokie]

You have not indicated the engine is running poorly or missing. If it is thats a different story.

I would do the simple things first. Manually manipulating the governor linkage is easy and costs nothimg. It could simply be sticking due to a buildup of grass clippings or dirt.

If that is not the problem you can move on to fuel and/or ignition..

Dan

 

[The Evil Twin]

I too would look at the governor first. Especially if there is no miss or sputter to the engine operation.
If there is, and the governor operates normally, I would start with ignition issues on a Kholer.

 

[lugbolt]

many folks can't "hear" a dead miss....a trained ear can hear it just fine, but many who aren't, can't. Runs on one cylinder, sounds perfectly fine to a lot of folks.

governors and linkages on the kohlers have never been problematic. to my knowledge or in my experience-unless someone has messed with them Briggs is a different story....