John Deere Z535M engine surging

[wavinwayne]

The governor keeps the engine constant while the blades are engaged. When at idle with the blades disengaged, you're having a lean condition from a fuel blockage in the carburetor somewhere. This is a very common occurrence. You notice how I use the the word "occurrence" instead of "problem?" That's because it's not a problem if you like carburetors.

To me, a carb may as well be a nuclear reactor. Of all the things I've worked on over the years, carbs never made the list.

 

[wavinwayne]

This might be highly controversial, but Whip City Wrencher did a recent video and BG44k cleaned a spark plug pretty good vs others. Project Farm also did a video as well. Maybe you can run some in the engine as a try and see thing. I might invest in it as well.

https://www.amazon.com/BG44K-BG-44k-PLATINUM-New/dp/B07PXCTPV7/ref=sr_1_7?crid=6YVZKRGR80GG&keywords=BG+44k+PLATINUM&qid=1640170145&sprefix=bg+44k+platinum%2Caps%2C69&sr=8-7

Thanks, I'll look into it.

 

[wavinwayne]

Possibly. Gasoline engines run hotter when lean which is not good for them. You have an increased risk of burning valves and blowing head gaskets.

I would try running some fuel cleaner through it and see if that does the trick. I like Berryman's B12.

I'm going to try either Seafoam, Techron, or a similar product. I might have a small engine mechanic look at it eventually if nothing I try helps. I'm not confident enough to tear into the carburetor myself.

 

[supton]

To me, a carb may as well be a nuclear reactor. Of all the things I've worked on over the years, carbs never made the list.

See if you can go to partstree.com or similar, and find an exploded view of your carb. If it's complicated and a mess of parts... then leave it be. if it doesn't look too intimidating, maybe take some of the engine covers off and put your eyeballs onto the various rods, levers and springs, and see if it still looks intimidating.

Usually OPE carbs aren't that complicated, a handful of parts. And if it doesn't work after a "rebuild", rebuild it again (and again) until it does. [Did that on my ATV, got one part wrong on the butterfly valve, and it barely ran. Until I finally gave in, pulled it off, took it apart, looked at the part I put on wrong, and the schematic, and said "is it possible I have it in the wrong order?" Ran after fixing that.]

 

[Soft Cars]

To me, a carb may as well be a nuclear reactor. Of all the things I've worked on over the years, carbs never made the list.

They are amazingly simple. If you have an hourglass shaped passageway that narrows down in the middle, air has to speed up to get through that passageway. When the air speeds up, that creates a low pressure area. Low pressure is what a vacuum is. If you take one end of a straw and insert it into that low pressure area while the other end of the straw is inserted into a pool of liquid, the low pressure area will suck the liquid into the passageway. At that point the air and fuel will turn into a mist and that mist goes into the combustion chamber where it explodes. When the mist explodes, that forces the piston down and turns the crankshaft.

 

[Cujet]

Miracle in a can is not likely to fix that. You prob have a clogged idle jet (or a bad gasket) . It probably won't idle well.

Interestingly, in this video, she shows the top of the carb plate that can be removed, and maybe a little very careful wire and spray tube action from a can of carb clean, run down through the idle jet will unclog it. At 3:30 and again at 8:50 she shows the cover that will get you access to the idle jets.

 

[The_Eric]

The governor keeps the engine constant while the blades are engaged. When at idle with the blades disengaged, you're having a lean condition from a fuel blockage in the carburetor somewhere. This is a very common occurrence. You notice how I use the the word "occurrence" instead of "problem?" That's because it's not a problem if you like carburetors.

Not exactly true. Your typical small engine governor is going to try to yank the throttle closed all the time. The higher the engine speed, the harder it's going to try to close the throttle. It's spring tension on the throttle that works to open it, which is why when the engine is off and you advance the throttle a little, the carb snaps WOT. Think of it as a tug of war between the governor and throttle spring.

When the engine slows - either from load or a poor mixture, the governor exerts less tension against the throttle spring, which allows the throttle spring to pull the throttle open. Then the engine speeds up, the weights that operate the governor fly out and make the governor arm pull harder which should bring things back into equilibrium.

When the engine is lean at idle as in this case, it's trying to maintain a speed, but can't, so it dies off a little, the governor let's off, then the throttle spring is exerting more force and pulls the throttle back open and the process starts again when the engine speeds back up

 

[wavinwayne]

Update: I mixed a can of Seafoam with 5 gallons of zero ethanol gas and ran that through the mower over the last couple of weeks. It isn't surging anywhere near as bad as before. I will probably do one more can of Seafoam and let it be.

 

[supton]

The air filter "fix" I tossed at mine lasted one mow, then it came back. With nothing to lose (and no replacement gaskets on hand), I elected to do a brake cleaner rebuild. Remove carb, shoot as much cleaner as I can through anything and everything, and hope for the best. If I fail, it looks like it's $30 for another carb on Amazon--I didn't see how to remove the fuel bowl on mine. Until it acts up again, I'm leaving alone.

 

[gman2304]

I would run a few ounces of Berryman B12 through it before doing anything else. It stopped my Kawasaki 160V from surging after one dose. Couldn’t hurt.