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I have a Cub Cadet pushmower, Model 94M with Engine Model - 1P70MO.

Trying to address a surging issue - seems to surge when hot but not constantly. Periodically will almost stall and when surging doesn't burn clean. Can make it better with partial choke.

What I've done:
Re-cleaned carburetor
Verified spark plug @ .030

Plug/oil/air filter/fuel filter new late last year. Fuel is fresh from a month ago, started after purchasing this fuel but I had also removed and cleaned carb at same time.

What I'm planning on:
Using fluid (carb cleaner? Fuel injection cleaner?) where carb meets block to rule out air leak - based on issue when hot and partial resolution with choke.

Should I re-examine the carburetor? Initially I thought this happened when hitting bumps and was leaning towards week spring on float and was thinking about rebuild. Any way to test the governor?

Thanks in advance!

-Eric

Videos of son mowing neighbor's yard - you can hear surging:

https://youtu.be/CJSRtrVsX0o

https://youtu.be/QcxtFUXv53M

Use WD 40 from a trigger gun, not a aerosol can.
The propellant could go POOF
Usually a surging is issue is a clogged main jet.
Type that engine model # into parts tree.com and look at the carb in the diagram, it should show you where the jet is to take it out and clean it.

A vacuum air leak is most likely at idle speed and that's the best time to check for air leaks.

Scrubcadet10 said:

Use WD 40 from a trigger gun, not a aerosol can.
The propellant could go POOF
Usually a surging is issue is a clogged main jet.
Type that engine model # into parts tree.com and look at the carb in the diagram, it should show you where the jet is to take it out and clean it.

Click to expand...

Thank you!

I can't find an exploded diagram on partstree.com for Cub Cadet 951-10310 (carb model # for Cub Cadet 12A-94MC010) but I'll keep looking.

Your theory makes perfect sense as I bought this mower from a family member last year and found maintenance hasn't been a focal point. Last summer it wouldn't stay running and when I opened the carb it was full of gum and varnish - cleaned it and it ran like a champ until a few weeks ago. I did run it dry for the winter and cleaned the carb again this Spring but I was hesitant to disassemble the top portion of the carb and remove jets - just saturated with carb cleaner.

-Eric

SeniorCitizen said:

A vacuum air leak is most likely at idle speed and that's the best time to check for air leaks.

Click to expand...

Pardon my ignorance - is idle speed when the mower isn't under load? My assumption is the engine will always run about the same RPM, so no "idle" as in a car, and the governor keeps the RPMs constant based on load?

-Eric

llebcire said:

Pardon my ignorance - is idle speed when the mower isn't under load? My assumption is the engine will always run about the same RPM, so no "idle" as in a car, and the governor keeps the RPMs constant based on load?

-Eric

Click to expand...

You are correct, and it seems as if you have an engine that some student engineer spent long hours dreaming up a way to screw things up. It's not your fault because those have been around for quite some time.

Technically there is a lo RPM idle and a hi idle RPM. It seems yours doesn't have lo RPM idle the engineer deemed not necessary and only has hi RPM idle with idle in this case "Yes" meaning no load. Therefore the test I mentioned earlier at lo idle cannot be preformed.

llebcire said:

Thank you!

I can't find an exploded diagram on partstree.com for Cub Cadet 951-10310 (carb model # for Cub Cadet 12A-94MC010) but I'll keep looking.

Your theory makes perfect sense as I bought this mower from a family member last year and found maintenance hasn't been a focal point. Last summer it wouldn't stay running and when I opened the carb it was full of gum and varnish - cleaned it and it ran like a champ until a few weeks ago. I did run it dry for the winter and cleaned the carb again this Spring but I was hesitant to disassemble the top portion of the carb and remove jets - just saturated with carb cleaner.

-Eric

Click to expand...

Type that engine model # into parts tree.com and look at the carb in the diagram, it should show you where the jet is to take it out and clean it.

1P70MO

Scrubcadet10 said:

Type that engine model # into parts tree.com and look at the carb in the diagram, it should show you where the jet is to take it out and clean it.

1P70MO

Click to expand...

Thanks!

That's the same diagram as in the owner's manual - I was looking for something more detailed.

Carburetor comes apart very easily. I've had the two circled components out each time I clean it - assuming the jet in the middle (left on image) is the main? The one on the right of the image is controlled by the float.

I'll clean it again and get some new fuel.

-Eric

Took carburetor apart this morning before mowing (still same fuel). Everything looks clean (more pics below) but I noticed the innermost gasket, against the block, is torn (bottom left corner).

Is this likely the issue as excessive air is entering the combustion chamber? I also notice there's fuel in the air filter element whenever I open it.

And - I can't seem to find the gasket by itself. Where else should I look for the part? Would rather not use high temp silicone but I will.

-Eric

More pics. Runs better with choke slightly engaged.

-Eric



https://youtu.be/wKJCHiAkdtg

Scrubcadet10 said:

Use WD 40 from a trigger gun, not a aerosol can.
The propellant could go POOF
Usually a surging is issue is a clogged main jet.
Type that engine model # into parts tree.com and look at the carb in the diagram, it should show you where the jet is to take it out and clean it.

Click to expand...

This was the issue - eventually figured it out!

I went as far as replacing the carb with a knock-off from Amazon, which barely ran at all, then I found a YouTube video showing a different jet. I assumed the jet I needed to clean was visible with the bowl removed, however I found the video below and cleaned the jet under the black plastic cap with a stand of wire - felt something dislodge - now it runs like a champ!

Thanks for the advice.

-Eric