Columbia 159cc walk behind won't stay running

Bounje

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So I am trying to get my 159cc Columbia (MTD built) mower to run but have been having problems diagnosing the issue.

The mower starts but then bogs down and cuts out. Usually within seconds of starting if not right away. Once out of several test starts it ran maybe 4 seconds then choked up and restarted itself for a second or two before cutting out. It was running longer time periods (~30-60 seconds sometimes) before cutting out prior to removing the carb for cleaning.

The fuel in the tank is premium grade gasoline about 4 months old with stabilizer added at the pump. I drained the stuff from the tank and added fresh from the can.

It sounded like a carburetor issue so I cleaned that three times with carb cleaner (thought maybe I had missed something and tried again between startup tests) and once with an ultrasonic cleaner. It seemed pretty clean when I first pulled it off: no rusting , discolouring, or gumminess. Bought and installed a replacement carb just to ensure there was no hidden issue I was missing there...

Not sure if I'm missing something crucial on the reattachment of the carb. There is a black gasket that I recall going onto the front of the carb before the metal piece covers it. I've done my best to align the black gasket with the holes on the front of the carb. Made sure all the levers on the carb are correctly positioned. Could the long black gasket behind the carb being incorrectly positioned could cause these symptoms?

Tested the gas cap vent to see if it was restricting air intake and it was so I replaced that but I had been cracking the cap during testing after I learned this could cause the same symptoms.

I dumped the fuel in the tank (rinsed tank with fuel; blew out with compressed air), changed spark plug, and burned out/shook muffler empty. Fuel filter was changed early last year and the beginning of this season; blew it out but didn't seem clogged. Changed the fuel line because it was cracking a bit on the outside and worried that it was breaking down inside the line.

Also tested the ignition coil because it looked rusty and I've been running this mower for a few years. It tested out of spec so I replaced that.

Despite all of this I am still getting the same symptoms and the mower won't stay running after start up.

At the end of the day I am not mad if I can't get this mower running again as it was $200 CAD and I've run it for 3 years+. I went out and bought a Troy-bilt 159cc because it has the same engine type. At least I have a running mower now. I can use any of the newly bought parts on that in the future and harvest spares from the Columbia.

It would be nice to pinpoint the issue so I can learn from that. At the very least I have learned quite a bit about the machine through this process.

Any thoughts on next steps or testing?
 

StarTech

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Depending the MTD engine it may have an internal tank filter that needs cleaning. Don't know which P series you have but I am guessing a P65. Both filters may have been used at some point.
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Bounje

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Yeah, it's in tank. I didn't use carb cleaner but used air on it.

It's a plastic filter you think using carb cleaner is a good idea?

It was replaced spring of this year.
 

StarTech

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Carb cleaner is not usually safe for use on plastics.
 

Bounje

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Yeah, I have taken the fuel filter out a couple times wiped it off and blown it out. Not sure if it has some sort of clogging on the screen but fuel does run through it so I don't think it's an issue.
 

Bounje

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The last spark plug had black carbon build-up on it, if that info is useful. Will check engine number
 

Bounje

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Okay, looks like it wasn't anything major.

I cleaned the original carburetor again with a wire, carb cleaner, and compressed air and that seemed to do the trick. The mower is running again.

So the culprit was a clogged carb, clogged gas cap, and non-functional ignition coil.

One interesting thing to note on this model of MTD carburetors is that there is an internal screen inside the fuel intake tube. This can be important to know when cleaning this area of the carb.
 

Bounje

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Looks like the engine number is 5X65MU
 
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