757, Half power

[DT86]

A friend down the road called yesterday and says his 757, The zero turn Deere not the Boeing jet... is only operating at half it's usual power. And dies when the blades are turned on. (25 hp v-twin Kawi, 1000+ hrs)

After a quick inspection we determined it was only firing on one cylinder. We installed 2 new plugs and fuel filter. Still one dead cylinder. Its getting gas and spark. Can't figure this one out. Here is a pic of the new plugs, the difference is obvious even after less than 10 mins run time. Plug on the left is from non firing cylinder, it is discolored from being soaked in unburnt gas. The other has a burnt look due to combustion.




I guess the next things on my list are a compression test and new plug wires??
Help!!! Anyone?

 

[Zork]

Improper valve seating should cause popping from either intake or exhaust. and fuel is an indicator there is enough compression/vacuum to draw the fuel into the cylinder -unless it is injected. Is it fuel injected?

Before you do a compression check can you safely remove the wire from the dead cylinder while the engine is running and modulate the wire at different distances from the plug and see if the plug fires and the cyl recovers? This will indicate several things from bad plug (doesn't fire under load) to ignition wire coil issues.

 

[DT86]

Improper valve seating should cause popping from either intake or exhaust. and fuel is an indicator there is enough compression/vacuum to draw the fuel into the cylinder -unless it is injected. Is it fuel injected?

I looked up the valve clearance and found that it should be .004" -.006" on both intake and exhaust. As far as the seat, with 1,000+ hours its possible.

No it is not injected, it has a twin barrel carb.

Another thing I found out today is that this engine has had new rings. I just don't know when.

This is driving me :confused2:

 

[DT86]

Anyone?

 

[Zork]

Did you try my diagnostic proceedure with the plug wire???

 

[DT86]

I think I did what you mean. If not help me understand.

It has a strong spark at varying distances from the plug to the wire. But now what?

Keep in mind i swapped sides with the old plugs and it made no difference, then got new ones.

Also the compression tested good. Someone else mentioned a bent push rod.

 

[Zork]

This is not the case for a mechanical malfunction. Sometimes when plugs or wires begin to fail they appear OK or test OK but under load they don't work properly and removing the wire from such a plug (or dead cylinder) while the engine is running and modulating the distance of the gap between the wire and the plug causes the dead cylinder to fire indicating either the plug (usually) or the wire.

A bent push rod should be easy enough to check with a visual confirmation that the valves are moving and the lash is correct.

 

[DT86]

That is kind of what I thought. I think I'll recheck the valves and have him get some plug wires. Thanks.

 

[Yellowfever440]

Well, the bad news it is a mechanical problem, more bad news you will prolly have to replace one of the heads. If the plastic shroud around the fan has never been removed and the grass blown out around the jugs then I would tell you it has over heated one of the heads and the valve guide has seized to the valve and the aluminum head expanded and the guide started moving in the head. Come on machines that were in the earlier serial number. Take the valve cover off and turn the motor over and make sure all the valves move the same, check the jugs to make sure the grass isn't built up, if it is it prolly over heated the head.

 

[BeGray]

Any resolution? My JD757 (25hp Kawasaki w/ 250 hrs) just started showing identical symptoms. Thanks!

 

[DT86]

Any resolution? My JD757 (25hp Kawasaki w/ 250 hrs) just started showing identical symptoms. Thanks!

Well I just called to ask him what he had done to fix it. He said the carb was gummed up and also he had a bunch of gunk in the fuel tank. He had someone clean tank and installed a carb kit and it runs fine now. Good luck! Oh and welcome to TBN, it's addicting.

 

[BeGray]

Resolved my issue. Turns out that it was a pair of bent push rods on the left side of the engine. I've now mowed for 5 hrs after replacement and it seems to run fine. The valves must have gotten stuck...maybe due to overheating. Hopefully it won't happen again. Thanks for all the help!

 

[Gator6x4]

Most Kawasaki engines have something called an igniter. When this goes bad it displays the same symptons you describe. You say the compression checks good so I don't think you should keep going down that road by checking for bent push rods or a sticking valve. The compression test would have revealed this. Igniters are expensive. You may need to discuss the problem with a Kawasaki Dealer to see if there are tests the dealer can conduct on the igniter to determine if it is bad.

 

[Dutch445]

Resolved my issue. Turns out that it was a pair of bent push rods on the left side of the engine. I've now mowed for 5 hrs after replacement and it seems to run fine. The valves must have gotten stuck...maybe due to overheating. Hopefully it won't happen again. Thanks for all the help!

I would expect some buildup of grass/debris in that engine shrouding preventing proper cooling. Would advise anyone
with that series of ztrac to be diligent in trying to prevent the heads from overheating, causing the push rod and guide issues.

 

[ddivinia]

I just had my 757 go south. Two bent pushrods on the #2 cylinder. I pulled it apart and the exhaust valve guide has backed out. I really don't have time for a broken mower. I ordered a new engine and I'll fix the old one up over the winter.

I still kinda want a JD 997...

D.

 

[gregmartin]

I just had my 757 go south. Two bent pushrods on the #2 cylinder. I pulled it apart and the exhaust valve guide has backed out. I really don't have time for a broken mower. I ordered a new engine and I'll fix the old one up over the winter. I still kinda want a JD 997... D.

I have a 05 JD z-Trak 997 , I love it never had any trouble with it. I think you will love it to

 

[bucaneere]

I have a 757 and had engine running on one cylinder and this is what I found. Checked the valve clearance ok, checked ignition ok, checked compression ok, then noticed after removing air cleaner that visual inspection of the carb showed fuel not entering one jet. Removed the carb, cleaned with Berryman cleaner, run bread tie wire through jets after dissembling, purchased new float, needle valve, gasket set, reassembled and engine runs perfect. I believe the bowl gasket had failed plus some fouling from unleaded fuel...hadn't had problem for 12 years...I think the fuel has a way with the gaskets...fortunately Deere didn't use but the one bowl gasket.