[cboudet]

So you bought a used engine from someone who stated it "ran great but keeps blowing head gaskets..." I am not sure I would label an engine that keeps blowing head gaskets as a "great runner" but let me leave that for another discussion.

Common issues with the FH721 and related series engines is overheating due to clogged or plugged cooling systems, the problems associated with overheating (such as warped heads) and loose valve guides which can result in bent pushrods and so on.

Granted, this wouldn't cause it to die like it was shut off...
If you want to go further into that discussion I can do so, but it relates more to a mower that struggles under load... It will die if you push it and engaging a PTO will certainly do that, but if you disengage immediately it should recover even if sluggishly which would lead me to further search in the areas of overheating due to crud buildup and loose valve guides and warped heads and such... But again even with a warped head it would still run warmed up, it just won't run good.

So perhaps the issue is electrical, perhaps a wire is shorting out against the frame someplace but then wouldn't it do the same when cold? Might be worth looking underneath at the clutch connector... If that comes loose or if it has 3 wires and (I think) the ground wire is disconnected then it will kill the mower when engaging the clutch but also when moving the stick(s) because of the logic circuitry, still odd that it won't do it when it's cold...

Which leads me back to the ignition coils.
You state you replaced these, if I recall correctly.

Wow, a lot to think about here. I have tried to disengage the pto right away and it still dies.
I got new coils yesterday. I had checked spark before and have spark on both cylinders, but I don't know if a coil that is failing can recover that quickly.
I am going to check disconnecting the kill wire first, then removing the fuel shutoff solenoid to see if it still happens and go on from there.
Thanks again.

 

[J. Baker]

I had checked spark before and have spark on both cylinders, but I don't know if a coil that is failing can recover that quickly.

It cannot.

 

[sidemouse.ii]

Wow, a lot to think about here. I have tried to disengage the pto right away and it still dies.
I got new coils yesterday. I had checked spark before and have spark on both cylinders, but I don't know if a coil that is failing can recover that quickly.
I am going to check disconnecting the kill wire first, then removing the fuel shutoff solenoid to see if it still happens and go on from there.
Thanks again.

That is good. Often these V-twins can run without load on one cylinder and the operator barely notices, but as soon as a load gets put on the story changes. To test coils we can do so before ordering new ones, do this with the engine off:
Disconnect either side spark plug wire, then start the mower.
See if it runs, even if crappy.
If it does, cut it off, reconnect whichever side and unplug the other side.
See if it runs again.
If it won't run on either side then your faulty coil is the one that's still connected.
Granted, it is recommended to replace both coils at the same time.
This is also something where I just might use the coils off an old engine if it's the same part number.

On another note, aftermarket carburetors for the FH721V run just under $35...
One of these comes with all the gaskets (even some you won't need), and the linkage connectors:

Carburetor Kawasaki (15004-0757,15003-7094, 15004-1005) FH721V for sale | eBay

Get the best deals for Carburetor Kawasaki (15004-0757,15003-7094, 15004-1005) FH721V at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!

www.ebay.com

I replaced the one on mine with that one, I would suggest replacing all the cheaper parts (under $100) one at a time before tearing into the cylinder head to replace a gasket. So that would be coils and carburetor, I think you've replaced the rest of things, might check that black rubber breather / PCV tube as well.

 

[cboudet]

That is good. Often these V-twins can run without load on one cylinder and the operator barely notices, but as soon as a load gets put on the story changes. To test coils we can do so before ordering new ones, do this with the engine off:
Disconnect either side spark plug wire, then start the mower.
See if it runs, even if crappy.
If it does, cut it off, reconnect whichever side and unplug the other side.
See if it runs again.
If it won't run on either side then your faulty coil is the one that's still connected.
Granted, it is recommended to replace both coils at the same time.
This is also something where I just might use the coils off an old engine if it's the same part number.

On another note, aftermarket carburetors for the FH721V run just under $35...
One of these comes with all the gaskets (even some you won't need), and the linkage connectors:

Carburetor Kawasaki (15004-0757,15003-7094, 15004-1005) FH721V for sale | eBay

Get the best deals for Carburetor Kawasaki (15004-0757,15003-7094, 15004-1005) FH721V at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!

www.ebay.com

I replaced the one on mine with that one, I would suggest replacing all the cheaper parts (under $100) one at a time before tearing into the cylinder head to replace a gasket. So that would be coils and carburetor, I think you've replaced the rest of things, might check that black rubber breather / PCV tube as well.

Good to know.
The wiring diagram shows the oil pressure sensor is connected to the carburetor fuel solenoid at the key switch. Could it be telling me that I have low oil pressure?

 

[sidemouse.ii]

Good to know.
The wiring diagram shows the oil pressure switch is connected to the carburetor fuel solenoid switch. Could it be telling me that I have low oil pressure?

Hmmm...
How was it running before you swapped carburetors?

 

[cboudet]

Hmmm...
How was it running before you swapped carburetors?

Great when cold.
I think I am onto something here.
If the oil sensor (which was plugged before) is telling the engine it has low oil pressure,it can activate the fuel solenoid and kill the engine. I am going to temporarily bypass the solenoid and see.

 

[J. Baker]

Good to know.
The wiring diagram shows the oil pressure sensor is connected to the carburetor fuel solenoid at the key switch. Could it be telling me that I have low oil pressure?

Does the machine have an oil pressure light?
I doubt it has a SENTRY system. Very few machines do.
I think you are misinterpreting the wiring diagram.

Mr. Mouse will lead you on a wild goose chase worse than you’re already on. Be warned.

 

[cboudet]

Ok, I took the solenoid out and plugged the hole temporarily. Now I can drive forwards and backwards and it doesn't die, but as soon as I put the pto on, it dies.
I am thinking I need to check those wires and connections again

 

[J. Baker]

You need to be more methodical, and stop skipping all over the place.
You need to complete some tests you were asked to complete and report back. Such as if disconnecting the engine controls (kill wire) from the machine eliminates the problem.

 

[Valk]

Are the NEW coils installed now?

 

[cboudet]

Does the machine have an oil pressure light?
I doubt it has a SENTRY system. Very few machines do.
I think you are misinterpreting the wiring diagram.

Mr. Mouse will lead you on a wild goose chase worse than you’re already on. Be warned.

Yes, the machine has an oil pressure light.
I am not misinterpreting anything.
You look at the diagram.

 

[J. Baker]

Yes, the machine has an oil pressure light.
I am not misinterpreting anything.
You look at the diagram.

Yes, you certainly are misinterpreting the diagram. The diagram shows exactly what I expected it to.

That shows that both the carb solenoid and oil pressure light both receive power from the same terminal of the ignition switch. They are not connected in ANY way. Only share the same power terminal. The oil pressure switch provides ground path to turn on the light if oil pressure is lost.

 

[cboudet]

You need to be more methodical, and stop skipping all over the place.
You need to complete some tests you were asked to complete and report back. Such as if disconnecting the engine controls (kill wire) from the machine eliminates the problem.

Yeap, that is my next test.
I got a little excited there.
Answer me this:
Is the oil pressure sensor (basically a switch) normally on or off?
Thanks

 

[J. Baker]

Yeap, that is my next test.
I got a little excited there.
Answer me this:
Is the oil pressure sensor (basically a switch) normally on or off?
Thanks

Forget the oil pressure switch. It only runs the light. It’s not related to anything.

 

[cboudet]

Yes, you certainly are misinterpreting the diagram. The diagram shows exactly what I expected it to.

That shows that both the carb solenoid and oil pressure light both receive power from the same terminal of the ignition switch. They are not connected in ANY way. Only share the same power terminal. The oil pressure switch provides ground path to turn on the light if oil pressure is lost.

Baker, basic electrical wiring tells you that if two wires share the same terminal THEY ARE CONNECTED.
So is the ground path from the sensor normally open?
Thanks

 

[J. Baker]

Baker, basic electrical wiring tells you that if two wires share the same terminal THEY ARE CONNECTED.
So is the ground path from the sensor normally open?
Thanks

The carb solenoid is independent of the oil pressure switch. Last time I’m saying it. NOT RELATED. Forget the oil switch.

You obviously do not understand basic DC power flow. 🙄

 

[J. Baker]

Tell you what. Go unplug the oil pressure switch and run it. It will still run just like it always has. Won’t change a thing.

 

[cboudet]

Tell you what. Go unplug the oil pressure switch and run it. It will still run just like it always has. Won’t change a thing.

I guess you don't like to be told you are wrong.
You meant to say that the two circuits are not related, but you said they are not connected in the wiring diagram and there is where there was a misunderstanding.
So, I removed from the circuit both the solenoid and the oil sensor, and I was soo happy because for a while I was able to burn rubber and engage the pto....
Until it warmed up.

 

[J. Baker]

I guess you don't like to be told you are wrong.

I wasn’t wrong.

You meant to say that the two circuits are not related, but you said they are not connected in the wiring diagram and there is where there was a misunderstanding.

You misunderstood. Not me. My response was clear. You seemed to think the oil pressure switch somehow powered the solenoid. It DOES NOT.

So, I removed from the circuit both the solenoid and the oil sensor, and I was soo happy because for a while I was able to burn rubber and engage the pto....
Until it warmed up.

Told you so.

 

[cboudet]

Are the NEW coils installed now?

No, not yet. I want to disconnect the kill wire first and see what happens, but I get of path.