# L120 dies after a while



## tonyennis (Jun 10, 2012)

My JD L120 (20 HP Briggs Intek V-twin) would run for about 15 minutes, then die. Choking helping for a minute or two.

I changed all the filters and oil. I rebuilt the carb. Today, it ran for about an hour, then died in a similar fashion. Since fiddling with the choke seemed to help, I don't think it's a safety switch issue.

(That being said, I can no longer get off the mower without it the engine stopping. I am pretty sure I used to be able to push both pedals down and pull up the "lock" switch located on the left side of the console, and dismount. Now that doesn't work. I'm sure the blades were disengaged.)

I also replaced a magneto coil; I replaced one side and the engine exhibited the same issue. So I swapped the remaining old for the old one I replaced, reasoning that it would be unlikely for both to be bad.

I can't be sure, but I don't think the engine is running at full power, and it almost seemed like it has a miss in it. It runs a little rough when it starts.

edit - it has a miss, I am sure. It sounds wrong.

So, any ideas on what I should do?


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## wjjones (May 28, 2010)

It could be that brake safety, or trash in the carb bowl it may need a good cleaning.


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## tonyennis (Jun 10, 2012)

I just rebuilt the carb. It is reasonably clean now.

Will the choke keep the engine running if the issue is that the safeties are removing the spark?

I've seen postings saying that there's a way to completely remove the safety devices from the equation; do you know what it is?


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## wjjones (May 28, 2010)

I just cleaned the carb out on one of my push mowers 3 times, and finally had to just run it until it burned the trash through on its own. I would not remove the safety switches but you can use a jump/ bypass wire to figure out which one is bad. I thought the same, and there have been manytimes I have been glad I didnt remove the safety switches. I always just unplug one switch at a time, and bend a piece of wire into a u shape to jump one side of the switch right back into the other. This should bypass it to figure out which switch is bad I am sure there will be other members that will have tips, and tricks you can try to single out the bad switch.


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## tonyennis (Jun 10, 2012)

I certainly have no intention of bypassing the safety switches permanently. I'm trying to isolate the problem. I can almost see a case where a switch is shorting every time the mower vibrates (many times a second!) causing the engine to miss.

I do know there has been a change because I can't get off the mower without it stopping even when I set the brake appropriately. Maybe it is a separate issue; I don't know. It worked the last time I mowed.

I just don't know much about engines and I'm trying to avoid paying someone to come get the mower and service it - it will be hundreds of dollars.


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## tonyennis (Jun 10, 2012)

I just pulled the connector off the seat switch. The engine runs just as poorly but now I can get off the mower. So I surmise this is a coincidental issue; the seat switch is bad. I am surprised pulling the connector off allows the motor to start.


Ahh but the engine shut off when I engaged the blades... I thought it was the load on the engine - but perhaps this is what the jumper wire does.

But the engine still didn't run well without the blades engaged.

This is frustrating - I don't know enough to trouble-shoot this, and I don't know what I don't know.

edit - both magneto coils show between 560 and 585 ohms.


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## wjjones (May 28, 2010)

A seat switch would be a good place to start it sounds like it is stuck in the bypass position if it is letting the engine start. Is your brake locked when you get off the mower, and it still runs?


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## tonyennis (Jun 10, 2012)

Before I disconnected it, no, the mower would shut off. Now that it's disconnected the mower continues to run when I get off.

However, I'm pretty sure that switch isn't my problem. The engine is running too rich - it only runs at all if the choke is closed , or nearly so. It used to run with the choke completely open.

So somehow, too much fuel is being delivered, as far as I can tell.

I verified the spark plug gap is correct. Both were dirty, even though they're new.


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## wjjones (May 28, 2010)

I would say carb float, or fuel pump if yours has a pump? If its not getting enough fuel then one , or the other is not working correctly. If its to much fuel then the float is sinking causing the carb to overload, or its out of adjustment.


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## tonyennis (Jun 10, 2012)

I have another idea for tomorrow regarding the carb.

Would you happen to know what the wire connected to the magnetos is for? (not the one that goes to the spark plug... I *know* what that one does! :lmao

EDIT - also, there's a short rubber tube that connects the carb to the intake manifold (?). I think it may be called a breather tube. The tube has some cracking, perhaps from dry rot. Could this be a contributing factor?


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## mowerfan741 (Jun 9, 2012)

wire tat goes to the magneto is a ground or kill same problems with mine check push rods and valves too sounds dumb but one could be bent like mine was hope it helps


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## tonyennis (Jun 10, 2012)

I removed the ground wires, no change in behavior. While examining an exploded diagram of the carb, I saw a gasket in the 'top' of the carb I didn't know about. Took the carb back off, disassembled that part of the carb, and found the gorilla who put the part on crushed the rubber gasket. There are 7 holes in the gasket; 4 are kinda small. Two of the small ones were blocked by crushed gasket material.

I replaced it, reassembled, and the mower started right up.

Unfortunately 15 minutes later, the engine surged a few times, then died.

So I have solved *a* problem, but not *the* problem.

Is there a chance an intermittency in the seat switch (it also went bad over the last 3 weeks) is somehow causing me to lose spark?


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## bigl22 (Sep 16, 2003)

check the following, vent hole in gas cap, cooling fins under engine cover to be clean and free , debris in tank and lines. blow clear from pump back, fuel filter , all will act up -- check for weak ignition coil and valve free play , put in new spark plugs


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## bigl22 (Sep 16, 2003)

try moving around in seat while driving, if seat springs wear down, you may not be centered on seat switch enough, , bypas all of the safety switches one at a time


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## tonyennis (Jun 10, 2012)

Bigl22, I've tried experimenting by moving around on the seat, I could not change the mower's behavior by doing so.

Fins are clear, I cleaned the fuel cap's vent hole, The fuel filter is new. I checked the magnetos, they seem fine. Spark plugs are new and properly gapped.

The reason I want to disable *all* the safeties is that once the engine stops running it won't start until the engine cools. So if I disable them all in one shot (hopefully there is a simple way of doing this) and the mower misbehaves I know the safety system is not involved and I'll save a lot of time.

Do we have an opinion about the solenoid at the bottom of the carburator? Can it be overheating and failing?

I'll blow air into the fuel line to see what happens. 

I don't know how to check the valves.


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## bigl22 (Sep 16, 2003)

you can check valves clearance cold by removing covers and checking gap; disconnect battery and screen cover and turn engine by hand with proper size socket on ratchet or breaker bar , yes, carb solenoids do go bad, i can't remember how to test them, ask on[ weekend freedom machines]. and gardenweb too -- a few old geezers can probably remember better than i do. Leland


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