Question about Mtd Yard - Man 160cc, 21" Self - Propelled Lawn Mower

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Yard-man model 12a-979L401 won't start (9 years old)

I put fresh gas, checked oil, new air filter, new spark plug and connected wire, nothing happens when I try to start it. Manual says to adjust gap on spark plug - don't know what that means, or clean fuel line, how do i do that?

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My dad always taught me, rest his soul, that basic 101, if you have gas getting to spark, SOMETHING out to happen.
I'll ask a series of questions and propose some possible solutions. Hopefully we'll crack this mystery. Warning, this might be a tad lengthy... ha
1. Is the spark plug firing?
To check the coil that sends spark to your spark plug and the plug itself:
You can remove the spark plug from your engine and reconnect it to the spark plug wire while it just lays on your mower. pull the starter rope (make sure you're holding down the kill lever on the handle). Look at your plug end as you pull the rope.
Got spark? If yes, go to the next step, flagged ***. If no, look at the end of your spark plug that would go into the engine. The "L" shaped finger should be gapped from the small circular shape on the plug... this is the "gap". Your manual may provide specs on how wide this gap should be. If there is no gap, your plug won't work properly. The "L" shape is a soft metal and can be bent... create the proper gap. Try the test again to see if the plug is sparking. If not, you may have an issue with your coil.
***Yes to spark. Let's look at the gas issue now. OPTION 1. I will tell you that in my experience, water in gas is a major culprit for a mower not running. You've replaced all the filters... good.
I'm not sure of your mower, but most models have a "bowl" bolted to the bottom of the carburator. Sometimes moisture can get in the gas, get trapped in the bowl and won't go away or won't allow gas to get to the spark. Loosen the bolt... it's ok if gas from the bowl spills from this, the bowl doesn't hold much gas and it won't drain your tank. Plus, this means your carbuator is allowing the gas from the tank to the bowl. As you are looking at the gas spilled on the mower deck, see if there are beads of water in it. As you know, water and gas doesn't mix. This would be a tell tale of the problem. I would carefully remove the bowl from the carb and wipe it dry, then reassemble the bowl.
To be on the for sure side that you have no more water in your system, you could disconnect your fuel line from the gas tank and drain it out. Use a jar or container... you can see water in the bottom of it. You can reuse the gas too... just don't include the water!
OPTION 2. If your carb and tank are now H2O free and you're still getting to results, you may have a clogged jet on your carburator. This little pin-hole passage allows gas to pass through to the spark. Sometimes a mower sitting up a while, can cause a laquer effect to gas and it can block this passage. Removal of the carburator from the engine is required and a simple pin can be pushed through this passage to knock a "plug" out.
Geez I hope I didn't miss anything! ha
Good luck to you... I hope it's a quick and easy fix.

Posted on Aug 26, 2009

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I realize that you changed the spark plug. However, did you also check to see whether it had spark?
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Possible Causes Corrective actions
Unit will not start Control handle is not engaged Engage control handle spacer.gif spacer.gif
Spark plug wire is disconnected Connect spark plug wire spacer.gif spacer.gif
Fuel tank empty or stale fuel Replace with clean, fresh gas spacer.gif spacer.gif
Blocked fuel line Clean fuel line spacer.gif spacer.gif
Faulty spark plug Replace, clean, or adjust gap spacer.gif spacer.gif
Engine flooded Wait to restart, do not prime spacer.gif spacer.gif
Air filter filled with dirt or debris Replace or clean air filter

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