[Iwin]

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.

I had an efi walker with a Kohler on it that ran great for about an hour under load, then it would run out of power and was really hard to start. This machine was under warrantee. They replaced tons of parts trying to fix it. It ran great until you mowed an hour so the shop could not duplicate the issue. They finally did a leak down test and it failed so they put on a new engine and it's been great ever since.

 

[J. Baker]

Good morning Baker.
I decided to follow your advise and will probably be getting a new mower.
I also decided that I want to learn a little more and I will be continuing to play with the old engine.
I don't know if you remember that I have a second engine with a good running top end, so I would like to keep this thread open and occasionally come back to it with a question as I work on the engine.
I also wanted to ask you about the compression test. You said you would prefer if the reading was around 100. I was reading the manual and think the minimum acceptable pressure on that engine is 60 psi.
I am attaching a page of the manual.
Please comment on it.
Thanks for everything! View attachment 531397

You most certainly can continue on!

About that spec, there are a couple possibilities. It could be that engine has a compression release (which slightly opens the exhaust valve during compression via a weighted device on the cam) thus lowering compression to make spinning the engine with a rope start or small starter easier. Or, the spec is a misprint. I’ve not seen a spec that low in any modern engines that I can think of, so let me dig around and see what I can find. I can’t believe that spec is correct though. 57 psi is extremely low. I bet it has a compression release.

 

[J. Baker]

The Kawasaki FH721V has a compression release. That’s why the minimum spec is so low. But that may also explain the 90 psi on the “good” side. I didn’t think about it using a compression release on that engine.

Still a lot of other issues to address on that motor. Doesn’t explain the dying. It’s possible the spring on the compression release is broken and it is actuating when it isn’t supposed to, but it should be completely random. This issue is very consistent.

 

[NewFarmGuy]

So, if the heads and valves are ok, or can be repaired, this engine could possibly be saved. If the compression is restored and it still exhibits the same surging, loss of power when hot and shutdowns its still possible the electronic control module could be bad.

I’m convinced had I not replaced mine when I did, and if I kept running it in with those same symptoms that I too would have gotten excessive heat damage, warping heads, burnt valves etc.

My very novice point is what was the cause of the affect. Which is which?

We wont know unless the damage gets repaired to that engine and it’s tested again.

I dont like throwing parts at problems either, but based on my Kawasaki 721 engine problems and the lengthy thread about it from all ya’all I checked everything that was suggested and ran out of possibilities until someone said it fixed their motor. And…it fixed mine. i just couldn’t let my machine sit at the mechanics another 3 weeks in the summer.

I’m just throwing out the suggestion that the electronic control module could have been the root cause?

I struggle with this site on my iPhone so I cant find the specific post but I thought the original engine had already been replaced with another used one that ran the same?

I’m very grateful for you all! I now know so much more about my machine because of you.

 

[cboudet]

So, if the heads and valves are ok, or can be repaired, this engine could possibly be saved. If the compression is restored and it still exhibits the same surging, loss of power when hot and shutdowns its still possible the electronic control module could be bad.

I’m convinced had I not replaced mine when I did, and if I kept running it in with those same symptoms that I too would have gotten excessive heat damage, warping heads, burnt valves etc.

My very novice point is what was the cause of the affect. Which is which?

We wont know unless the damage gets repaired to that engine and it’s tested again.

I dont like throwing parts at problems either, but based on my Kawasaki 721 engine problems and the lengthy thread about it from all ya’all I checked everything that was suggested and ran out of possibilities until someone said it fixed their motor. And…it fixed mine. i just couldn’t let my machine sit at the mechanics another 3 weeks in the summer.

I’m just throwing out the suggestion that the electronic control module could have been the root cause?

I struggle with this site on my iPhone so I cant find the specific post but I thought the original engine had already been replaced with another used one that ran the same?

I’m very grateful for you all! I now know so much more about my machine because of you.

I read your thread also.
This engine replaced one that kept leaking oil regularly even after seals were replaced 3 times over the years. But that engine ran great.
Unfortunately I broke one of the threaded ears of cylinder #2 (the ones that hold the muffler bracket to the cylinder head) in the process of removing it from the mower, so I have to find 2 #2 cylinders to replace them on both engines.
Thanks.

 

[cboudet]

Hello again!
I've been busy and had not had the chance to remove the heads on the kawasaki.
If you remember, cylinder 2 had (zero) compression and cylinder one had 80.
Cylinder one was allowing the engine to run fine for a short time and as it warmed up, it died.
When I removed the head on cylinder one, the valves and springs appeared normal to me, other than a big color difference between the intake and the exhaust. Also the stem of the intake valve has a lot of carbon deposits.
Here is where my lack of experience limits me, because I can't figure out why.
I uploaded a couple of pictures.
If anyone can provide their expertise I would appreciate it.
Thanks!

 

[Scott87]

In the first pic is the exhaust valve seated? It looks like the valvle seat has moved in that pic. When the head overheats the valve seat will drop out and theres most likely other damage to the head. It should be replaced if this is the problem.

 

[cboudet]

In the first pic is the exhaust valve seated? It looks like the valvle seat has moved in that pic. When the head overheats the valve seat will drop out and theres most likely other damage to the head. It should be replaced if this is the problem.

Yes the valve was seated. I do not see the valve seat out of place.
I will be lapping the valves and will check the seats again after cleaning the carbon deposits.
Thanks

 

[Justin Hightower]

Any scarring of they cylinder walls? Still see cross hatches?

 

[cboudet]

No they are smooth. one of the valves had some corrosion. I polished the stems and it's gone.
I found 4 out of 5 screws that hold the head were stripped and have Heli coils in them.
Tomorrow I will test the threads to see if they hold the required torque.