MTD Yardman 139cc - Wouldn't start after cleaning the deck. Carb issues.

canflyboy

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  • / MTD Yardman 139cc - Wouldn't start after cleaning the deck. Carb issues.
I have a 139cc Yardman push mower that failed to start after I tipped it on it's side to clean the bottom deck.

At best it would start for a few minutes and then die. It's only a couple of years old and I thought I'd share my fix on this unit.

First I checked for spark by taking the plug out, grounding it against the case and spinning the engine with the starter rope. The little blue spark ensured me that my ignition was working so I checked the fuel out next

Take off the plastic top cover (4 screws) remove the air filter and remove the air filter housing (two nuts and a bolt). This will give you better access to the carb and will allow you to pinch off the fuel line with a pair of needle nose vise grips.

I took off the carb bowl with the 10mm wrench on the bottom. I momentarily unpinched the fuel line to allow fuel to the carb. I then moved the float up and down to make sure fuel was coming into the bowl and stopping when the float was pushed up. This all checked out.

I then decided to remove the carb and give it a good cleaning. To remove the carb, you need to disconnect the fuel line and two linkages. One linkage is for the automatic choke. That's the first butterfly valve you'll see when looking into the carb. To remove the choke linkage, I had to remove the plastic "flag" that serves as an automatic choke. To remove this from the engine, I had to remove the recoil (three bolts from the top) and the housing. Then I had to remove the magneto which gave me access to the bracket that held the "flag" to the mower. Once this is removed, you can easily remove the choke linkage.

The throttle linkage was much easier. Just rotate the plastic throttle arm on the carb to a position where you can lift off the linkage. The spring will also need to come off.

Now you can pull the carb off the two mounting studs and clean it.

I removed the float mechanism and checked to make sure everything was clean. Holding the carb upside down, I sprayed carb cleaner down the float jet and main jet. Let then soak for a bit and then blew them out. I then took a wire from a twist tie and pushed it through the jet passages to make sure they were clear.

Re-assemble the carb, attach the linkages and mount the carb. Attach fuel line. Re-assemble the magneto with .010 clearance. Attach blower housing, recoil unit and outer plastic housing.

Started first pull. There was obviously dirt (or varnish) somewhere in the carb. It's a bit of a chore to get the carb off the mower, you may be able to blow it out from the bottom without having to remove the carb from the mower.

Hope this helps someone. When I did a google search , I noticed others having the same problem with this mower and it most likely was a dirty carb. Apparently, these engines don't like bad (old) fuel and varnish in the carb is a problem. Not sure if my problem was dirt or varnish, but it was the carb.
 
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