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Hello again,
Sorry for all my questions but until I am more familiar with the "ins and outs" of this machine I thought it better to ask before then after... the previous owner told me that the way he shuts the motor down on the 721D was to back the throttle all the way and then turn the key off-- his words. When I do this, the engine sputters a bit then shuts down. Before I purchased the machine from him, I did check with the mechanic who worked on it and he said he had told the previous owner that he needed to replace the fuel solenoid as the motor should shut down as soon as you turn the key off. I purchased a replacement solenoid to fix the problem, but before I tackled it, I wondered if this is a straight swap job or does it need to be " adjusted" after installation with tools I don't have... the basic solenoid body looks the same as does the wiring between the new and the old but the actual shaft and covering appear different between the two... I will try to take and upload some pictures of the new and the old one tonight but thought I would throw this question out for anyone with any suggestions.. .. as always, thanks for your time..

geoff

geoff said:

Hello again,
Sorry for all my questions but until I am more familiar with the "ins and outs" of this machine I thought it better to ask before then after... the previous owner told me that the way he shuts the motor down on the 721D was to back the throttle all the way and then turn the key off-- his words. When I do this, the engine sputters a bit then shuts down. Before I purchased the machine from him, I did check with the mechanic who worked on it and he said he had told the previous owner that he needed to replace the fuel solenoid as the motor should shut down as soon as you turn the key off. I purchased a replacement solenoid to fix the problem, but before I tackled it, I wondered if this is a straight swap job or does it need to be " adjusted" after installation with tools I don't have... the basic solenoid body looks the same as does the wiring between the new and the old but the actual shaft and covering appear different between the two... I will try to take and upload some pictures of the new and the old one tonight but thought I would throw this question out for anyone with any suggestions.. .. as always, thanks for your time..

geoff

Click to expand...

Here are pictures of the installed solenoid and the replacement one... thanks

There are two diesel solenoids that Kubota uses...
A Fuel ON solenoid and a Fuel OFF solenoid... I have one of each type on two engines ...
The one you are showing is a fuel ON type... It holds the fuel shut off lever in the rack to the ON position, then when the key is turned off it looses power and allows the shut off lever to return to the off position.

The only adjustment that could be there is the position you mount it as to the distance it needs to pull to turn the fuel on...

Actually I'm surprised the solenoid is at fault... when that type goes bad it fails to turn the fuel ON, or fails to hold the fuel ON.
When that system fails to turn the fuel OFF it is usually the return spring, that pulls the shutoff lever to the OFF position, check if that spring is broken :smile:KennyV

Hi Kenny,

Thanks again for all your great information... its really appreciated!! I do have some follow up questions that your reply generated. You said that you have two kinds of solenoids, one that is a fuel OFF and the other that is a fuel ON.. you also said that the one I had was a Fuel ON.. but I wasn't sure which one I took the picture of, you were referring to: the new one that was not installed or the older one that was shown installed, or are both the units I posted pictures of the same type? I am presuming that they are not interchangeable--correct? Based on your answer, I might have to return the one I just purchased for the other model--right? Thanks for any more information you can provide.. you have been a real help. Do you know of any service manual available for purchase that I can learn more about this machine?

geoff

russ could likely point you toward a manual... he and a couple others here have the same mower...

Both of the one's you pictured are fuel ON.
The fuel OFF has only 2 wires,
The fuel ON has 3 wires....

The only online manual I know of is: The Mower Shop, Inc. - Grasshopper Lawn Mower Parts - Parts Diagrams for Grasshopper Mowers
It is a parts manual and some other helpful information... You could also keep an eye out on eBay...:smile:KennyV

I have replaced the solenoid but now having a problem. After I installed it, the engine struggled a bit to start but when I shut the key off, it shut off promptly. However, when I buttoned everything up, I wasn't able to start it up again.. sigh, If I manually pull the threaded rod attached to the solenoid backwards in towards the solenoid, the engine will start up, but as soon as I let it go, it shuts off. I thought I just needed to thread more of the rod into the body of the solenoid but the rod was threaded as deeply into the solenoid as possible. When I compare the bodies of both solenoids, the new one is shorter than the old one... my question is this: Intuitively, I think I need to cut off some of the threaded rod. Am I correct or am I missing something? When the engine is started, am I correct in the belief that the threaded rod should PULL the rod in towards the solenoid? And when I turn the key off, and the solenoid is de-energized, the spring will push the threaded rod out and shut it off? Any help is appreciated.. If that is correct, then I am thinking as you said before, the solenoid is just not getting power, which means that the old solenoid probably was working fine... Thanks

geoff

That solenoid has three wires :
A GROUND wire.
A PULL wire, (This is a high current winding, energizing a strong magnet that temporarily overcomes the shutoff SPRING)
A HOLD wire, this is a low current, weaker magnet that holds the fuel ON.

When the 'key' switch is turned OFF power is removed from the hold windings... The SPRING then puts the fuel shutoff in the OFF position.
The threaded rod is only there to make the mechanical connection, and it has to be the correct length to FULLY OPEN the shutoff when it is energized & allow it to be FULLY closed when it has no power applied.
THAT solenoid ONLY pulls it never pushes... The strong field Pulls to overcome the spring, and the weaker field pulls to Hold.
:smile:KennyV

KennyV said:

That solenoid has three wires :
A GROUND wire.
A PULL wire, (This is a high current winding, energizing a strong magnet that temporarily overcomes the shutoff SPRING)
A HOLD wire, this is a low current, weaker magnet that holds the fuel ON.

When the 'key' switch is turned OFF power is removed from the hold windings... The SPRING then puts the fuel shutoff in the OFF position.
The threaded rod is only there to make the mechanical connection, and it has to be the correct length to FULLY OPEN the shutoff when it is energized & allow it to be FULLY closed when it has no power applied.
THAT solenoid ONLY pulls it never pushes... The strong field Pulls to overcome the spring, and the weaker field pulls to Hold.
:smile:KennyV

Click to expand...

When the 'key' switch is turned OFF power is removed from the hold windings... The SPRING then puts the fuel shutoff in the OFF position.
The threaded rod is only there to make the mechanical connection, and it has to be the correct length to FULLY OPEN the shutoff when it is energized & allow it to be FULLY closed when it has no power applied.

UPDATE:

Something is still wrong.. while I was waiting to see your response, I figured out the concept you mentioned above... that when energized, the current cause the solenoid to pull back the rod allowing the fuel to pass.. when de-energized, the magnetic field is lost, and the spring allows the rod to go back and shut the fuel off... however, this is what happens on my mower: I used a meter and confirmed that there was a ground, the black and that when the key is on, the Red wire has 12 volts. So far, so good. However, when I put EITHER the new or the old one in, and turned the key on, even without the rod attached, nothing happens. The portion of the solenoid that the rod attaches to, does nothing. It doesn't retract into the solenoid. However, IF I manually push the rod with the Key ON, the solenoid will HOLD the rod in the retracted position. And, when I shut the key off, it does push out. SOOO the problem appears to be, why won't the rod retract when the key is turned ON? I even thought that maybe the key needed to not just be in the ON position, but might have to be in the IGNITION position, the one you have to turn and hold the key into, but when I did that, I got the same results... no movement of the solenoid rod. But it will hold it IN, if I first manually push the rod in.. then the magnetic field appears to be strong enough to keep it there until I turn the key off... in addition, the instructions that came with the new solenoid say that if the old solenoid was not equipped with a return spring, as the new one is, ( my old one does not have a spring) then I am supposed to CUT another spring on the throttle body.. THAT makes me nervous!!! sounds like its the point of no return... besides, if the new solenoid won't retract the rod when energized, then whatever the problem is, I don't know that the old solenoid is bad... I did test both solenoids after they were off with an omh meter and got about the same readings when I tested between the White and BlacK and between the RED and the Black.. sorry to be bothering you Kenny but I sure would appreciate it if you have any brilliant ideas given this new information... geoff

I would also be happy to call you or give you my number if thats more convenient ... and if its allowed
THAT solenoid ONLY pulls it never pushes... The strong field Pulls to overcome the spring, and the weaker field pulls to Hold.
:smile:KennyV[/QUOTE]

Hello ... not a bother at all... I have worked many hours on this type control system, and they can at times be a challenge... My system uses 'murphy' gauges to shut the engine down with this type hold ON solenoid.

If you think it will help PM me your phone # I'll call you and see if we can get yours figured out.... :smile:KennyV

For others that may be following this...
The PULL windings draw a LOT of current, actually more than the windings can handle ... they can ONLY be energized for 10 to 15 seconds...
When the key is in the on position only the HOLD windings get power....
With the key turned to the START position the PULL windings get power.
That overcomes the return spring and allows the HOLD windings the opportunity to to keep it in the fuel ON position.

The PULL winding will ONLY get power while the starter is cranking the engine...
The HOLD windings get power with the key in the ON & start positions... :smile:KennyV

KennyV said:

For others that may be following this...
The PULL windings draw a LOT of current, actually more than the windings can handle ... they can ONLY be energized for 10 to 15 seconds...
When the key is in the on position only the HOLD windings get power....
With the key turned to the START position the PULL windings get power.
That overcomes the return spring and allows the HOLD windings the opportunity to to keep it in the fuel ON position.

The PULL winding will ONLY get power while the starter is cranking the engine...
The HOLD windings get power with the key in the ON & start positions... :smile:KennyV

Click to expand...

Just sent you my phone number...

The LAST installment of this post I think:

First of all, THANK YOU Kenny!!! for anyone who has followed this post, I spoke with Kenny this afternoon as I was desperate to get the mower fixed and mowing today.. and time was running out. I had put an email into Grasshopper's Tech Support but wasn't sure when I would hear back from them. In the meantime Kenny and I spoke about the issue of the solenoid. I had power to the RED terminal when the key was turned to the ON position,( not the crank position) and had a barely perceptible movement of the shaft of the solenoid. However, when I did crank the engine- I got nothing, nada, zilch. No movement of the rod of the solenoid. But if I manually pushed in the rod, with the key in the ON position, it would HOLD the rod in the retracted position and when I turned the key off, it let it go back to the extended or OFF position.

It was Kenny's idea that there was another fuse, other than the ones in the fuse box, which I had already determined to working, that might be blown. He said there was another IN-LINE fuse coming off the Starter Solenoid that powered the WHITE terminal when the engine was turned to CRANKING position. Sure enough I found that fuse with Kenny's help. It was a 20 AMP fuse and was definitely DEAD. Feeling I had discovered the problem, I drove down to the auto parts store to get a new 20 AMP fuse. En route, Dick from Grasshopper returned my call. He confirmed what Kenny said. The red terminal will be hot when the key in the ON position, and the WHITE terminal will be off. When the engine is cranking, the opposite occurs. The WHITE is hot pulling an increased load, compared to the RED, to PULL the solenoid's rod back, overcoming the spring on the rod. When the key returns to the ON position, the WHITE goes DEAD and the RED HOLDS the rod in the ON position, until you turn the key off and the engine shuts off.

I had previously used an Ohmeter to test the terminals on both the old as well as the new solenoid and found them both to be in specs.. before I hung up with Dick, he said one more key piece of information. The 20 amp fuse that blew SHOULD have been a 30 AMP fuse!!! which might explain why it was blown.

I replaced the blown 20 amp fuse with a 30 amp fuse and reinstalled the old solenoid. It did start up fine but when I turned the engine off, it didn't release the rod and the engine continued. I took it apart again and this time installed the new solenoid and BINGO it works perfectly!!!

Many thanks to Kenny for his patience , diligence and knowledge, as well as to Dick at Grasshopper for his insight into the correct amperage for the fuse. Had I reinstalled a 20 amp fuse, and it blew, I would have incorrectly assumed there was a short somewhere and begun a endless and useless hunt. Another positive note, the first time I took the solenoid out, it took me over an hour trying to find the correct sizes for the bolts, the wiring and the best way to get to everything. The final time- I took it out and replaced it-10 mins!!! Thanks again

Geoff

Where is the return spring ?

I have had the same problem as KennyV .

rswag said:

Where is the return spring ?

I have had the same problem as KennyV .

Click to expand...

This post is 5 years old.

I bet the return spring is still in the same place as it was five years ago. And if it isn't my 721d is a little over 5 yrs old so I was just checking. I don't have any external springs on the fuel linkage. Maybe mine is missing.
Thanks for your response anyway

I guess I should have said it better. No one is still around that started this 5 years ago. If you would start a new thread we would be more than happy to help. Me and my simple mind. Thinking everyone will understand what I type. Sorry about the confusion.