Z725 will not start unless coil ground is disconnected.

[ASBASS]

Hello, I am new to forum but it sure seems to be the place to get great help for Kubota equipment.

I have a Z725 with Kohler 25HP. Engine will not start unless ground wire to coils is removed. If removed the engine starts and runs fine.

The safety switches are working. If any of them are not made engine will not turn over. I know the coils are grounded by something. Where can I get a schematic. I assume when the switch is turned on it is suppose to open the ground to the coils. I recently replaced the coils and this started right after the new coils were installed. When the switch is tuned on does it open the ground circuit or does it energize a relay that opens the ground circuit?

Thanks
ASBass

 

[BruceP]

I work on many of these engines per week. (B&S, Kohler, Subaru-Robin, Generac, Honda, Kawasaki, chinesium-knockoff....etc)

Your issue is most-likely one of the 'safety' switches.

FIRST: You need to understand that there are MULTIPLE 'safeties'. Each of these are totally separate from each other.

• Some of the safeties prevent starter from cranking
• Other safeties will short coils to ground thus killing engine.

Understand that the starter-interlock may allow cranking the engine but the kill-wire is still grounded by the other safety circuit!!

-----------
To troubleshoot your issue use OHM meter. (battery MINUS disconnected and a rag lying over the battery-minus terminal for safety)

• Clip one lead of meter on the wire which is disconnected from the coils. (heading AWAY from the engine)
• Clip the other meter-lead to engine-case.

Your ohmmeter MUST show an open circuit in order for engine to run. (dont forget to put key in "run" position.) Simply troubleshoot to isolate what is shorting it to ground. (by pulling wires off of safety-switches one at a time) Again, it is most-likely a safety-switch. (seat, pto, neutral....etc )

As you narrow in on the issue, use your ohmmeter to validate and pinpoint the problem. It usually takes me less than 15 minutes to isolate a problem such as this with an ohmmeter.

-------------
BEWARE (I learned this the hard way)... on Vtwin engines, there may be a diode between the two coils on the kill-wire. Otherwise, the coils can interact with each other and kill the spark on the other coil.
To test for this as a problem.... only disconnect the wire from ONE coil at a time and see if engine runs on the other cylinder.

I assume you realize, when the cover is off the engine, the cooling is diminished.... so only run the engine long enough to do your testing.

 

[KUBOTA902]

Hello, I am new to forum but it sure seems to be the place to get great help for Kubota equipment.

I have a Z725 with Kohler 25HP. Engine will not start unless ground wire to coils is removed. If removed the engine starts and runs fine.

The safety switches are working. If any of them are not made engine will not turn over. I know the coils are grounded by something. Where can I get a schematic. I assume when the switch is turned on it is suppose to open the ground to the coils. I recently replaced the coils and this started right after the new coils were installed. When the switch is tuned on does it open the ground circuit or does it energize a relay that opens the ground circuit?

Thanks
ASBass
[/QUOTE

 

[KUBOTA902]

There are 4 relays on the left side of the machine. Pretty much under your left leg under the seat. One of them is the shut down relay for the coils. I have seen several of those relays fail. If I had to guess I'd say that's it

 

[ASBASS]

THANKS FOR THE INFO. I WILL DO SOME MORE TESTING TOMORROW,