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I have an older craftsman mower that sputters a lot. It does it particularly bad when it's cold, much less so when it warms up.
I've tried everything, fuel system cleaner, cleaning the carb, replacing the spark plug, using the freshest of fuel, changing the oil. Nothing seems to make any difference at all. It just sputters away. I'm not sure what else to try. Everything seems good, could it be something like a bad piston seal? I can try to take video of it so you can see/hear it. It's a 5.5 HP 21" mower. I'm not sure how old it is but I'd guess it's probably from the 90s.

l008com said:

I have an older craftsman mower that sputters a lot. It does it particularly bad when it's cold, much less so when it warms up.
I've tried everything, fuel system cleaner, cleaning the carb, replacing the spark plug, using the freshest of fuel, changing the oil. Nothing seems to make any difference at all. It just sputters away. I'm not sure what else to try. Everything seems good, could it be something like a bad piston seal? I can try to take video of it so you can see/hear it. It's a 5.5 HP 21" mower. I'm not sure how old it is but I'd guess it's probably from the 90s.

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read the similar threads below...with like problems

You said you cleaned the carb. Did you check the float level? Sounds to me like an engine which is running lean. Here's the procedure I recommend you follow in rebuilding and cleaning the carb. Get a replacement float needle and seat.


Needle and seat replacement.

Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. *Next check to make sure that the float does not have any liquid in it. *If it does, replace. *If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.

PS: *On the side of some Tecumseh carbs you will find a plastic cover. *Under this cover will be an idle jet. *Remove it and check to see that the jet is open both horizontally and vertically. *You should be able to push the old float needle wire through the vertical opening.

Here is a video of the engine doing what it does:

Maybe sputter is not the right way to describe it. Because it's not like it's dying or about to die. It just sounds like it's misfiring a lot. It still runs enough to use it pretty much normally. But I'd still like to get it purring if possible.

There is actually two sounds there. There is a misfire of the spark, but also a sputter, which in some ways sounds rich not lean. No sign of surging or a true backfire like what would be seen with lean. What is the operating rpm. Could be it is running too slow or fast and the carb isn't calibrated for that operation speed.

In person, it doesn't actually sound like two different sounds. I feel like the video might not be doing a super accurate audio recording of it, or maybe I was too close and the sound levels were messing with it. Or maybe my ears just hear poorly and this recording is actually giving the better more accurate account of what it's doing. *shrug*

Ok I'm back and still trying to fix this mower.
I checked the bowl and the bowl screw and the float. Everything looks perfect. The float didn't have a drop of liquid in it. No dirt anywhere. And at this point, i've run a TON of seafoam cleaning through it, in addition to having taken it apart a few times. Everything seems fine.

But I feel like what I'm going to say next is going to be a big key to the mystery.
So it stutters as it does in the video no matter how long you run it for. It gets more subtle as it warms up but it never stops...
UNLESS you tip the mower back. And I mean way back. Super unsafe-ly back, considering it's a running, spinning lawn mower. But beyond 45°*back. Then once it starts to choke, lower it back down. You get a biggggg cloud of smoke, and then all of the sudden the RPMs go way up and it runs perfectly, no skipping or stuttering at all, for a few seconds. Then after a while, it slowly settles back down to it's normal behavior, as seen in the video above.

A friend knowledgeable in small engines thought that odd behavior sounded just like a float that had fuel in it. So I took it off again to double check and it's definitely empty, everything looked nice and clean and there was only fuel where there should be.

I may try to get video of the problem magically going away when i tip it back, but that probably won't be until the end of the week at best. But if you have any thoughts, let me know.

starts & runs good till it gets hot, then sputter,die and will not restart till cold!!!

searsbsken said:

starts & runs good till it gets hot, then sputter,die and will not restart till cold!!!

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Nope those aren't really the symptoms at all.

Ok I took a video today of my sputter-stopper.

At the start of the video, it's just sputtering away. It sounds like it's only sputtering a little, but thats because I was 20 feet away recording with my phone. It actually sputters more than it sounds like it is.

Then I tilt it way way back. Maybe a little unsafely far back. Then is blows out a cloud of white smoke, almost dies, then revs up and runs perfectly for a short time without any sputtering at all. But after a while, it slows back down and returns to normal.


I'm hoping this behavior leads to some solid ideas of what specifically might cause it. This was what lead one person to think it might be a float with fuel in it. But i checked and the float seems to be perfect. What else would cause this odd set of behaviors?

What kind of governor does the engine have ?
Air vane or mechanical ?
Tipping it back like that prevents the float from stopping the fuel supply .
So I will go with a sticky float needle or a seat that has dropped down a bit.
The white smoke is oil so check the oil level and see if it feels thin.

Have you accidentally overfilled the engine oil?

bertsmobile1 said:

What kind of governor does the engine have ?
Air vane or mechanical ?
Tipping it back like that prevents the float from stopping the fuel supply .
So I will go with a sticky float needle or a seat that has dropped down a bit.
The white smoke is oil so check the oil level and see if it feels thin.

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I dunno. I wouldn't know by looking either. The float moves very freely and the needle does too. I don't know what this 'seat' is you are referring to though?

stevestd said:

Have you accidentally overfilled the engine oil?

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I put 20oz is just as the manual says. So I've only refilled it if the manual is wrong and it only takes 18oz, which I suppose is possible. But I also just changed the oil so I know its nice and clean and exactly 20oz. I warm them up before I drain the oil and I let it drip out for a longgggg time.

Being a Tecumseh engine and Tecumseh engines the float doesn't set level, Is the float adjusted at the correct setting. Remove the bowl and the gasket. insert a 11/64 drill bit opposite and parellel to the float hinge between the float and the carb body and the float should just touch the drill bit.

ILENGINE said:

Being a Tecumseh engine and Tecumseh engines the float doesn't set level, Is the float adjusted at the correct setting. Remove the bowl and the gasket. insert a 11/64 drill bit opposite and parellel to the float hinge between the float and the carb body and the float should just touch the drill bit.

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From memory, I think the float hangs down a lot more than that. How do you adjust the float level? I'm trying to find pics online but they're either with the carb fully assembled or fully disassembled, not many partially-dissasembled pics.

l008com said:

I dunno. I wouldn't know by looking either. The float moves very freely and the needle does too. I don't know what this 'seat' is you are referring to though?



I put 20oz is just as the manual says. So I've only refilled it if the manual is wrong and it only takes 18oz, which I suppose is possible. But I also just changed the oil so I know its nice and clean and exactly 20oz. I warm them up before I drain the oil and I let it drip out for a longgggg time.

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The 'seat' used to be a removable part with a tapered hole in it that the 'needle' would be pushed into to shut off the flow of gasoline into the float bowl. That's how the fuel level in the float bowl was regulated.

Some years back, carb manufacturers decided the seat portion of the needle & seat combo could be incorporated into the carburetor body itself. It's been awhile since I've seen a carburetor with a removable seat. So, you may not have one in your carb.

The smoke is oil smoke. Tilting the mower back like that causes all the oil to run to that end of the crankcase. The oil control ring on the piston can't handle that much oil and some gets by it into the cylinder where it gets burned.

l008com said:

From memory, I think the float hangs down a lot more than that. How do you adjust the float level? I'm trying to find pics online but they're either with the carb fully assembled or fully disassembled, not many partially-dissasembled pics.

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I think he's talking about when holding the carb upside down, i.e., with the float in its highest position. That's where you set float height, not with it hanging down.

You adjust float height by bending the tab that contacts the needle valve.

Related to this overall question, how can I figure out what carburetor and/or carburetor rebuild kit I need for my engine. The rebuild kits are cheap but whole new carbs are pretty cheap too. If I end up going that route, not sure which (of either) to get. I have the model number and manual for my mower, but it doesn't give any detail specs about the engine or carb. All it says is, if you think you're having carb problems, bring it in to a shop. I don't even know what year this thing is. I inherited it, it could easily be 20 years old.

So today I took the carb off and apart as best I could. Everything looked absolutely spotless inside, which isn't surprising considering how much carb cleaner I've run through this engine. And of course, when I put it back together, it actually runs worse now. It seems to be running at too low an RPM. There was one linkage that had a spring on it, and it was a bitch to get back connected. Does that sound right. That a spring controls the RPM of the engine, and if you stretch it, it will lower the RPM?



So I don't know what anything is called, but this spring seems to pull on this plated circled in yellow. And when I push it with my finger, the engine revs up. It still seems to spitter/misfire, but at least when i push on it, the RPMs seem right.

Soooooo did I just stretch out the spring? If so, how do I figure out what kind of spring to replace it with? Or am I totally misunderstanding what's going on here?

Also is there any kind of guide or instructions for exactly how to reassemble this thing if I ever decide to really go nuts with it? Including linkages, and positions of everything? That could be handy.

Your digital camera.

Well that only works if this 20 year old lawn mower hasn't already been re-assembled incorrectly. Which at this point I'm kinda wondering about.

Ok so last time I took it apart, I ended up mangling up one of the springs pretty good trying to reinstall it. It ran even worse after that. So I bought a new one for $4 on amazon and installed it today. The mower runs MUCH better now! It still runs like garbage when it's cold. But once it warms up, it runs much nicer, and at a much higher RPM than before. To be honest, it may even run worse now when it's cold. But the tradeoff is it runs better than it ever has since I've owned it, when it's warm.

These higher RPMs have brought back an old problem that had gone away... oil seems to leak out of the base of the filler tube, where it meets the block. It's not a fast leak... but its fast enough. And i'm sure some level of dirt is going in too. I don't think this is the cause of my problem, it's just a fresh new problem. The seal seems ok, I'm tempted to go to the hardware store and get an additional O ring and jam it in there to force a good deal. But then I got to thinking, a "regular" O ring might melt or burn from the heat?

Yes they are N buta regular O rings are neorpene.
About $ 2 from any mower shop.

Oil leak is fixed. I took the top off the mower, reseated the correct O ring, got some locking washers, the kind that grip, and re-bolted the top back on. No more flop or wobble, and the oil filler is now squished down firmly so no more oil leaks.


Now its just the engine issue. It really feels like the problem is TOTALLY different now than when I started this thread. The sounds are nothing like the movies any more. Now my inexperienced ear says it kinda just sounds like it is misfiring. Would that make sense? It does it less and less, the longer it runs. After 10-15 minutes, it barely does it at all. I don't know anything about it, so I suppose it could still be fuel delivery. But if it were a fuel flow problem, wouldn't it have been less of a problem when the mower was running at lower RPMs, and more of a problem at the new higher RPMs? Plus if it were a fuel delivery problem, what would cause the problem to go away once the engine heats up? What creates the spark that goes to the spark plug? Is it possible whatever that is, is bad on this mower?

You probably have done this already, my LT is so slow this morning I didn't read all posts. Have you run cleaner through the engine (Seafoam)? If not it is worth a try.

I've run so much seafoam through there, when you take parts of the carb apart, they are laughably clean. This spring, I even ran maybe 1/4 of a tank of about 50-50 gas seafoam mix. Which should be too strong to even start an engine like this but I got lucky. Before that, for like 2 years, I've been running it with a "normal" amount of seafoam in the gas. It hasn't ever seemed to have any effect at all.

Compression check?

*S*S*S*S*S*SOOOOOOLD!!!!!
Sold the mower today for $85. Out of my life thank god!!

I am still curious why it ran crappy while cold, if anyone has any thoughts? Would a compression problem go away when the engine warms up? What would a compression problem mean, what would be the actual "problem" that needs to be repaired?

Sounds as though it was running lean due to the sputter when cold. Did you ever shoot a shot of starting fluid, WD40 or a shot of gasoline directly into the carb to see if that would clear it up?

I think i sprayed carb cleaner into the air intake while it was running, not sure if that's what your suggestion. If not, then I'd say no.

Depending upon the carb cleaner, some will run an engine and some will not. Did it clear up at all, run rich or kill the engine? Not that it matters after the fact.

I think i used a can of regular old cheapo cleaner, and sprayed it in the air intake until the engine was almost dead, then let it come back, then repeated, several times. Didn't seem to have any affect when it was all done. While doing it, the cleaner would almost kill the engine.

Did you figure out your problem??

Well not exactly. Replacing the spring helped a lot, but it still sputters a lot when cold. But I have since sold the mower so it's gone. I'm going to start a new thread soon for the honda I have with it's own issues.