Kubota Z 125s Zero turn mower power surge governor hunting issues

[mcd40000]

Hey all! I could really use some help with my Kubota Z125s. Mower was purchased back in 2018 and has less than 200 hrs.

The throttle surges both at idle and under load, obviously worse under load to the point of the engine dying. The term I recently learned while researching is governor hunting and have been assuming the issues is an air/fuel issue. I’ve replaced the fuel filter, fuel pump, carburetor and even hooked up a temporary fuel tank to eliminate fuel line or tank being dirty. I have not done a compression test yet but pulled the spark plugs and tested them. I’m getting tired of replacing parts while the symptoms and issues persist.

Any ideas? I appreciate any and all suggestions.

 

[Outnumbered]

I had the welch plugs come off my carburetor on my Husqvarna with the 23.5hp Kawasaki engine around 100 hours and experienced the same issues you are describing. Purchased new ones on amazon for a couple of bucks. Replaced them and added a little nail polish to help keep them in place. No more issues 400 hours later.

 

[whitetiger]

Try moving the throttle lever partly into the choke position, and see if it starts to smooth out. If it does, you have a suction leak around the intake manifold gaskets where it bolts to the engine block.
You could also spray carburetor cleaner around the gaskets with the engine running and surging. If the surging clears up, it will also confirm the gaskets are leaking.

I would also pull the fuel shut-off valve and draw tube assembly from the top of the fuel tank and try to blow through it backward to see if it has any debris plugging it.

 

[GreensvilleJay]

Some governors have 2 or three springs. Have you checked whatever is on your engine ? ANY damage ,even a slight bend, can cause issues like 'hunting'.

 

[lugbolt]

don't mess with the governor

find the reason the engine is running lean and repair it. Could be vacuum leak, plugged jet, sticking shutoff solenoid, restricted fuel supply line/valve/pickup, etc.

address the supply side first as that is the most common issue. Second most common is old fuel plugging the carb. Third, air (vacuum) leaks.

 

[TECH101]

When was your first oil change ?

 

[TECH101]

Hey all! I could really use some help with my Kubota Z125s. Mower was purchased back in 2018 and has less than 200 hrs.

The throttle surges both at idle and under load, obviously worse under load to the point of the engine dying. The term I recently learned while researching is governor hunting and have been assuming the issues is an air/fuel issue. I’ve replaced the fuel filter, fuel pump, carburetor and even hooked up a temporary fuel tank to eliminate fuel line or tank being dirty. I have not done a compression test yet but pulled the spark plugs and tested them. I’m getting tired of replacing parts while the symptoms and issues persist.

Any ideas? I appreciate any and all suggestions.

Compression test, leakdown test, ignition test first

If all check out move onto removing carburetor and pressure testing it

 

[TECH101]

Compression test, leakdown test, ignition test first

If all check out move onto removing carburetor and pressure testing it

If all checks out.... move onto pluse pump vacuum test it, fuel flow from tank, pick up tube screen

 

[lugbolt]

real hard to say without seeing it in person but a surge is almost always a lean condition.

in 99% of those cases when I did them, it was almost always a carburetor issue-plugged jet, sticking shutoff solenoid, or restricted supply line. Rare to find an intake leaking on a Kohler although Kohler says otherwise. I just never saw it. In almost all of the surging engine issues on mowers, I had them fixed in an hour or less.

 

[whitetiger]

From his first post;

I’ve replaced the fuel filter, fuel pump, carburetor and even hooked up a temporary fuel tank to eliminate fuel line or tank being dirty

it was almost always a carburetor issue-plugged jet, sticking shutoff solenoid, or restricted supply line.

This is why I am leaning towards a vacuum leak at the intake manifold.