Engine Surge / Stall on John Deere EZTrak z445

[wmmiller1973]

Hello and thank you in advance to anyone who takes the time to read and offer suggestions.

I have a 2 year old Z445 zero turn mower with the Kawasaki V-Twin 25hp on it; it has just over 60 hours on it and the maintenance is current. A few weeks ago I was mowing (2 acre yard) and when I was almost done I noticed the throttle surging up and down during operation. It evened out after a few minutes and then I was done. I honestly forgot all about it, and when I got the mower out the next weekend, it started doing the same thing about 10 minutes in. It kept surging up and down and finally started bogging down when I hit thicker grass, and nothing bogs this mower down. Eventually it started dying and I had to choke it to restart it each time. It would die when I engaged the blades and finally started dying when I tried to move the mower even before engaging the blades. I let it cool off, then put it up and finished with another mower.

The next day I pulled the gas tank off and drained it; there were a few black specs in it. I pulled the (new) fuel filter and blew it out; there was a small chunk of debris in it. I checked the (new) plugs and they were black. I cleaned them up, checked the gap and re-installed. I checked the (new) air filter and it was very good. I checked the oil and it was perfect. I put everything back together and ran it hard for 10 or 15 minutes and it ran great with no surging or stalling. I thought the problem was solved.

The next weekend I fired it up and started mowing. The same problems happened as soon as I start moving forward after backing out of the garage. I mowed through it...at times it would die several times in a row and then would mysteriously run great for 15 or 20 minutes before the same cycle happened again. Each time I have to choke it to re-start and I am clueless what to do next.

I really appreciate any ideas anyone has.

 

[Fixemall]

You probably picked up some debris in the main jet, the surging is the governor basically revving the motor to compensate for the problem. All is not lost. Here is what you do...shut off gas with valve or gently clamp off line with vise grips, locate the carburetor bowl and mark it with a sharpie line extending from top of carb to bottom of bowl, next remove bowl and clean, spray carb cleaner into bottom of carb, remove fuel line at carb and spray carb cleaner in there as well, let dry and re install bowl using you line for reference, locate the main needle valve and turn it counterclockwise 1/2 turn, turn gas back on and restart. If problem still exists turn main jet out another 1/2 turn, if still surging you will need to disassemble and clean entire carb.

 

[tmajor]

There are couple of things, which come to mind;
My neighbor had an older Wheel Horse, which was doing the same thing. He never let me look at it, but another neighbor, who works on small engines did. He gave up! The tractor was ultimately sold, to another guy, who plays with them and is into lawn tractor pulling. He said it was something with the piston. Maybe. ??

My NAA didn't run too good for a while. The fuel bowl would have some specks in it, but always seemed to have fuel. Finally, I reset the point gap. ??
Sometimes, it seemed to be OK and other times it would start surging.

My Woods ZTR quit, or acted like yours. I replaced the fuel filter, which "looked good", but I couldn't blow through it. The new filter cured it.

Also, weed whacker and chain saw needed carb attention this season.

My thoughts are, that ethanol fuel is causing most of the problems.

 

[wmmiller1973]

Thanks for both replies so far. I will definitely look at all of your suggestions and let you know what I find.

 

[PapaPerk]

Sounds like fuel starvation. Check the obvious things like filters, fuel lines, shutoff valve etc.

Those engines run oddly I think when no load is applied. Part of their emission controls I think.

Have u cleaned the air filter?

 

[wmmiller1973]

PapaPerk - I put a new air filter on this season and I did pull it off and check it. It was very clean but I went ahead and blew what little dust out that was in it. I also checked the foam pad under it to make sure it was seating properly and it was good.

 

[Fixemall]

If you are not comfortable with carb disassembly you can always pull the fuel line just after the filter and run it on sea foam till it smokes like crazy and shut it down, reconnect line, give it a day and restart it. I have had varied degrees of success with sea foam and mildly gummed up carbs, my preferred method is to disassemble and run thru the ultrasonic cleaner, blow out with air and reassemble with new gaskets and seats.

 

[wmmiller1973]

Thanks again for all the replies...last night I fired it up and as soon as I started forward it stalled. I didn't even have time to loosen the gas cap to check for a vacuum. I fired it back up and it ran great for about 30 minutes in hard mowing conditions. Finally it started surging and I was able to rule out the gas cap vacuum...loosening it had no effect. I couldn't keep it running at all...I thought I would never make it back to the garage.

I am going to try cleaning out the carb main jet next.

 

[tmajor]

Before getting into the carb, I'd suggest pulling the fuel line off the carb and letting the gas run into a container for 10 -15 minutes, to see how the flow is.

 

[Tacman]

By chance did you check the fuel cap to make sure it was able breath? If its plugged, it will look like fuel starvation. Just clean the vent hole with a paper clip.