Engine Sputter

l008com

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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.
 

shiftsuper175607

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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.

read the similar threads below...with like problems
 

Rivets

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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.
 

l008com

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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.
 

ILENGINE

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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.
 

l008com

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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*
 

l008com

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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.
 

searsbsken

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

l008com

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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?
 
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