12.5 Kawasaki running rough

[crc]

Greetings,

I'm a lowly homeowner with a 2-year old Exmark Metro 36 with the 12.5 hp Kawasaki engine. The mower has probably 75 hours on it at this point. I'm having some trouble with the engine now that I've started the mower up for the season.

When I put the mower to bed last November, I changed the oil, cleaned the air filter, and drained the fuel (not to mention lubing everything and sharpening the blades, but that's not really relevant here...). Now fast forward to May. Today I filled up the tank and started it up. As usual, it started on the 2nd pull. No problem there. Unfortunately, my good luck ended at that point.

The engine surges and "ebbs" (if that makes any sense) very rhytmically. Every second or two, it surges to what I believe is normal full power for a bit, then loses power and rpms for a bit. This happens both at half and full throttle, and at idle as well as under load from the mower blades. As this happens, you can see the throttle linkage (I hope I'm using the correct terminology here...I'm a small engine newbie) moving back and forth. The throttle handle itself, of course, is not moving. So I guess I understand why the engine is surging -- the throttle is oscillating. But what is making the throttle linkage move?

In an attempt to fix the problem, I took off the carburetor bowl, looking for "gunk". It was perfectly clean. I didn't have any carb cleaner, so I didn't spray anything. I also took out the spark plug and tried to clean it (it was a bit black). No dice. I was going to drain the fuel, but I decided not to yet. The fuel is probably 2 months old, but it was immediately treated with Sta-bil after it was pumped. I'll drain it if I have to, but it's a full 5 gallons, and I'm lazy...

I'm not sure what to do next. From all my reading, these kind of symptoms can be caused by a bunch of different things: dirty carb, bad plug, bad fuel, dirty air filter, blocked fuel filter, etc. Is there one (or maybe two) of these that seem like the most likely possibilities based on my description? I would love to understand why the throttle linkage is moving back and forth without me touching it!

Thanks for any help anyone can provide. If I have to, I'll have the dealer look at it, but it's going to be a pain to get it there, because I don't have a trailer. I would much rather learn how to fix it myself.

Chris

[mower17]

I think if you would adjust the fuel air mixture a little it would stop. Turn that screw with the spring under it a little in each dirrection until it stops surging. The reason the throttle linkage moves is because since it is probably running lean, the engine starts to surge. When the engine slows down the governor speeds the engine up, then when it starts to overspeed, the governor slows the engine down. That's why it moves, the governor is just doing it's job. Hope this helps.

[crc]

mower17,

Thanks very much. I'm feeling very stupid right now, because I'm sure you're right. I'm pretty sure I caused my own problem by overtightening that screw (you mean it's not just for draining the carb at the end of the season??? Like I said, I'm a newbie.) As soon as the weather cooperates and I get a chance, I'll try backing that screw out.

Thanks again for your help. I know I won't make that mistake again...

Chris

[mower17]

Some engines have a screw just for draining the carburetor. If the screw has a spring on it and the end of the screw is pointed, then this screw isn't made to tighten all the way. It should be backed out about 1 to 2 turns. Of the screw looks just like any normal screw with no spring on it, then it is meant to be tightened all the way.

P.S. I have just been familiar with lawn mowers for a little over a year now, so I am a newbie too. These forums taught me a lot.

[crc]

Well, upon further investigation, I don't think the screw on the carburetor bowl controls the mixture. It does have a spring, but if it is backed out more than 1/4 turn, fuel leaks from the bottom of the bowl. I think it's just a drain screw.

So now I'm stuck again. I've read a lot, and I'm confused. The hunting and surging under load is described as usually caused by the carburetor, and usually caused by a blockage in the fuel and/or air inlets. Does this make any sense to anyone?

I managed to run the mower at about 1/2 throttle today to cut the grass. At 1/2 throttle, it doesn't hunt and surge, but the exhaust smells very nasty, like I'm not getting complete combustion or something like that.

Are there any obvious things I should be doing before I bite the bullet and figure out a way to get the mower to the dealer? I'd love to read a service manual, but I can't find one online. Probably because somebody wants to charge for it, right?

Chris

[mower17]

Then you might have a clogged fuel filter. It has happened to be before. My mower would only idle, it would kill at full throttle. Replace the fuel filter. It only costs $1 to $2.

[Hud]

Assuming you have the manual for your mower, you can:

1. Is it your original air filter with 2 years/75 hours? If so, it might be a good idea to replace it. Over time, the oil from the prefilter can ruin the paper element. It can still look good, but be bad, and a bad air filter causes the engine to run rich. And if it isn't the filter, you'll have a backup.

2. Did you drain all of the gas from the carb, tank, fuel filter? If so, you might want to replace the fuel filter. I have a 1995 Viking Hydro with 1200 hours, and have never replaced the fuel filter. But, I don't drain the gas on any of my equipment; I use Sta-Bil, and have never had a problem. I'd worry removing the gas would cause things to dry out that aren't meant to dry out.

3. Using your manual, you could go through the linkage, choke, and throttle. For example, with the engine not running, push the throttle to the choke position then make sure the choke is closed. Move the throttle from the choke position then make sure the choke is completely open. Make sure no cables have loosened and slipped. The choke not opening fully will cause the engine to run rich.

4. Using your manual, with the engine not running, adjust the governor to make sure it's set right. It is an easy thing to do.

5. You might want to replace the spark plug. If you've been running with an overly rich condition due to bad air filter, choke partially on, or whatever, you may have damaged the spark plug.

If none of the above get it going correctly, it's possible when you refilled the unit with gas, you stirred up sediment in the bottom of the float bowl, and sucked something into a jet or orifice.

And if you aren't comfortable with doing these things, you might be wise to let a dealer do it. You've got a great mower, and rather than you mess it up, a dealer could probably sort it out for you very quickly. At only 2 years/75 hours, it's not likely that it's anything major. Hope this helps, and good luck with it.

[Hud]

I should have mentioned in my post, you could try each item I suggested one at a time. If it were me, and based upon you saying you cleaned the air filter when you put it away and it appearing the mower is not getting "complete combustion" (running rich?), I'd check out the air filter first. If it has a prefilter, did you leave too much oil in it? A clogged air filter could cause the symptoms you describe. Then I'd check the choke. And I'd check the adjustment of the governor as a last resort: if it was working correctly when you put it to bed for the winter, it should be working now unless a spring fell off or something came loose.

As for the fuel filter, I suggested replacing it simply because I don't know what effect allowing a fuel filter to dry out would have on its effectiveness. It's obviously allowing gas to get into the carb.

Again, good luck.

[crc]

I just wanted to post an update on my situation. Taking Hud's advice, I went to the dealer and purchased a new air filter and a new spark plug. In addition, I spent a significant amount of time cleaning the foam pre-filter. I, of course, had cleaned the pre-filter last fall, and I soaked it in engine oil, just like the Kawasaki manual recommends. But while I can't remember for sure, I believe that I probably did not do a very good job squeezing out the excess oil before reinstalling the pre-filter. In fact, I actually found a small amount of engine oil inside the air filter housing. I think that, just as Hud had suspected, that there was too much engine oil in the pre-filter. That excess oil was not allowing enough air into the carburetor, which caused all of my problems.

In any event, after cleaning, oiling, and *squeezing* the pre-filter, I installed it on the new paper air filter, and reinstalled the whole thing in the engine. I also changed the spark plug. After all that, the mower started up on the 2nd pull as usual, and ran as smooth as can be. All is well now.

I want to thank everyone, especially Hud, for helping me with this problem. I continue to learn about small engines, and I know I won't make that mistake again! (Other mistakes, well, I can't promise anything...)