[cboudet]

Happy new year to all!
Thank for all the information and support you have provided to so many of us over the years.
I have a very used hustler Super mini Z with a Kawasaki fh680v that kept leaking oil, if it wasn't from the top crankcase seal, then from the bottom and I kept replacing seals every year until last month I found the mower sitting in a pool of oil and I decided to replace it with a used kawasaki fh721V that I bought on ebay as a good running engine that kept blowing head gaskets.
I replaced the head gasket and installed the engine. When I started it, it wanted to rev really hi so I set the governor according to the manual and now the engine throttles perfectly and runs smooth at hi and low revs, but in the process I found that it dies when it warms up.
The best description I can give is that when cold, I can go fast and climb a hill and the engine does not feel it, but after a minute,going forward from a stop will kill it and engaging the blades also. If I choke the engine, it starts right up again.
I have changed the carburetor, the fuel filter, the fuel solenoid, the engine does not smoke nor there is smoke in the dipstick.
I have no idea if the problem is fuel related (my gut feeling) or electrical,but I have read and searched here and in YouTube and have not been able to find a clue as to how to fix the problem.
I am hoping someone can suggest what to do.
Sorry for the long winded post and thanks in advance for reading it.

 

[cboudet]

Sounds like you might be dropping a coil. Pull one coil wire at a time when it starts acting up. If it dies when one wire is pulled then you know it's the other side that is going bad.

I ordered new coils and will be replacing them today, but if it is the coils, why does it start right up immediatety afterwards?
I almost seems like you turn the key off.
Thanks.

 

[cboudet]

Either the coils, or possibly ...

I had a persistent problem on a mower with a V-twin Kawasaki, long story short it turned out one of the plastic pieces that holds the throttle / choke linkage was cracked... In my case it was the choke linkage, the crack made it so the engine would choke fine but it wouldn't unchoke completely and thus as soon as it warmed up I'd lose power.

Specifically the metal rods that connect to the carburetor, when one of these plastic pieces breaks or is cracked it may still be connected but it's no longer operating the way it should... It's worth checking these up close visually, perhaps move the linkages by hand (you may have to operate the choke / throttle lever) to ensure smooth operation.


View attachment 530895

The linkage pieces in my carb are metal and are working fine. The choke does not get stuck and is working fine.
I also replaced the solenoid in the picture.
Thanks.

 

[cboudet]

When you got the engine, was it plug and play or did you have to mess with the wires ?

You did plug the wires back on to the voltage regulator ?

How old is the battery ?

At the battery terminals, do you have 13.6 volts ?

With the engine running at WOT, are you getting 14 + volts ?

The chances of 2 coils going out at the same time are like my chances of winning the Mega Million......
Unless one was already dead, then the other dying.....
Let us know how that works out......

Fuel valve fully open ?

If you are running saddle tanks, there could be trash partially blocking the pickup/valve at the bottom of the tank. The same goes for the valve to switch tanks if you have one.

Hi ho Hi ho............
.

The Fh721v is the same engine as the fh680v, just a couple of horsepower more and it was plug and play, so the voltage regulator is connected the same as the old one.
The battery is a year old, but it is strong. I have not measured the volts when charging, but that is easy enough to do.
I checked spark and have spark at both cylinders, the engine runs smooth until it dies.
I am using only one of the saddle tanks with no fuel valve, and fuel flows freely from the tank.
Checked the fuel pump and it is pumping.
Thanks.

 

[cboudet]

When it dies, you have to verify if it lost spark, or fuel.

My bet is either losing fuel, or something in the OPS system is malfunctioning. The latter is easy to test.

Yes, that is it. How do you verify if it lost spark or fuel when it is not running, and it starts again right away?
Pardon my ignorance. What is OPS?
Thanks

 

[cboudet]

The tank cap vent properly, and the fuel flows freely from the tank.
Thanks.

 

[cboudet]

Might be the choke linkage closes good, but it doesn't open completely...
Then it will start fine, and as soon as it warms up it loses power.
If a linkage is loose often the choke can be adjusted enough to still close...
But once you get moving the play in the linkage allows for play in the choke valve, and that play allows the plate to close even partially it cuts the air flow and thus power.



On the metal ones, inside the hole where the linkage hooks to the carburetor there is a hard plastic grommet piece or there should be... That was the problem I had, the little hard plastic grommet inside that hole was cracked and allowing linkage play. It was so minor, took me literally years to track it down.

I did the same as you, both coils, valves, fuel lines and filter, cleaned up underneath the covers real good... I was at wits end. I took it to a repair shop twice and it didn't act up when I was there, not even driving it around and engaging the blades but take it out to mow for a day and I couldn't even finish the first yard.
I replaced gas caps too, thinking if a gas cap vent was clogged.

When I replaced the carburetor...
Which at this stage I was just replacing parts, but it came with the new plastic pieces.
That's when I saw the problem.

Linkages on these things...

Here's the old thread on that FH721V:

FH721V suddenly started struggling

On my ztr today... I adjusted the valves about 1-2 years ago... It ran good for quite a while, but today while going up an incline it suddenly lost power. It will run "all right" without load but it does pop and sputter a little. Engage the blades and it pops and misses just a little more...

www.lawnsite.com

It would start awesome, run good for a few minutes and then the nonsense would start...

If there is one thing I am sure of is that the problem is not the choke. It works perfect, nothing cracked on the linkages. If it was choke related the engine would begin to run rough, but the engine runs smooth, warms up and dies under load.
Thanks.

 

[cboudet]

OPS= Operator Presence System

When it dies, don't try and start it. See if you can get the plug out of the bottom of the carb before restarting. If fuel runs out, it likely isn't running out of fuel, so it must then be losing spark.
Disconnect the engine kill wire from the machine after starting. Go run it. If it still dies, then you have a problem within the engine. If it doesn't it's an OPS problem or a short somewhere within the kill system. Remember, you may need to power the fuel cut off solenoid from another source as it may also be tied into your OPS system. Some are, most are not. Eliminate what it isn't, and you will find what it is.

I'm going to suggest you find a shop to take it to. It doesn't seem you know much about these systems and how they work. You really need a manual for both the engine and the machine with wiring diagrams so you can see how the two systems are tied together. Guessing isn't diagnosing.

I will disconnect the engine kill wire and check to see if check if I can find a short in the OPS, those are great suggestions.
For now, I am going to ignore the suggestion to take it to a shop. Not that I haven't thought about it.
BTW I have the service manual for the kawasaki and the mower. They do not have troubleshooting steps that help in my case.
Thanks.

 

[cboudet]

Does it die with PTO on or off

It runs fine until you load the engine with the pto or moving forward.

 

[cboudet]

I wish it was something as easy as that, but that is exactly how it feels.
No,the seat switch has been bypassed.
I can start the mower when it is cold and the engine runs perfectly smooth. It will move and climb an incline without feeling it, then after a minute or so,when it warms up, you try to move forward, backwards or engage the blades and it dies. I think it is something internal with the engine that when it warms up it looses all the power. I wander if a warped head will do that.
I did not get the parts I ordered yesterday, so I will have to wait until the weekend to work on it again because I work until 7.
Thanks

 

[cboudet]

And none of that would cause it to die suddenly as if the key was turned off.

I Read the old thread,
Thanks

 

[cboudet]

Parts arrived.
I will do some more checking befor I start replacing.
Can someone comment on this question that I have, at the end of the paragraph:
"I can start the mower when it is cold and the engine runs perfectly smooth. It will move and climb an incline without feeling it, then after a minute or so,when it warms up, you try to move forward, backwards or engage the blades and it dies. I think it is something internal with the engine that when it warms up it looses all the power. I wander if a warped head will do that."
Thanks

 

[cboudet]

Any possibility that when the engine over revved that it blew the new head gasket? Only thought about a warped head is that the engine might still run on one cylinder so missing vs shutting off completely.

Yes, I haven't over-reved it but don't think that the symptoms are those of a blown head gasket, and it doesn't run rough.
Thanks

 

[cboudet]

No.
Well, it could I suppose, but highly likely. And not within a minutes time, and not without being very noisy. Usually if a head is warped that bad and leaking you can hear it.

I think you’re chasing your tail.

Yeap.

 

[cboudet]

My tail.

 

[cboudet]

Just a thought. It sounds like the fuel mixture is leaning out when the engine warms up and stalls when its loaded. If you can choke it and it will start again I suspect a leak in the intake manifold between the engine side of the carburator and the engine when the engine warms up. Check for warpage or gasket that is thin, etc.
Also, I am assuing the carburator you replaced was new, not rebuilt?

I changed the carburetor, I robbed the old engine which ran great, it is not new.
Thanks

 

[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.

 

[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?

 

[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.

 

[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