JD L120 automatic surging
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Thread: JD L120 automatic surging

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    JD L120 automatic surging

    My L120 has been having some issues, I have the Briggs 20hp engine and ~620hrs on it. I inherited this tractor, and don't know too much about it, but i've been fiddling and fixing a couple things here and there.

    The newest set of problems started last week, I noticed after mowing about an acre that the front muffler was RED hot. Immediately after that, the service reminder came on and the tractor stalled. I was able to get it started again, but it began surging and continued unless I had the choke all the way up.

    From everything I've researched, it seems like this could be a gummed up carb. My problem is that I don't know anything about engines. Is there a guide that I can follow to taking apart and cleaning the carb? Is this something that an amateur can take care of or do I need someone with small engine experience?

    I would really love to learn everything I can about this thing and fix the problems myself (especially because the local power equipment place has a month long backlog). I'm going to change the oil tonight and check the fuel line, replace the fuel filter and see if that makes any difference.

    Appreciate the help!

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    Quote Originally Posted by ChickenMan View Post
    My L120 has been having some issues, I have the Briggs 20hp engine and ~620hrs on it. I inherited this tractor, and don't know too much about it, but i've been fiddling and fixing a couple things here and there.

    The newest set of problems started last week, I noticed after mowing about an acre that the front muffler was RED hot. Immediately after that, the service reminder came on and the tractor stalled. I was able to get it started again, but it began surging and continued unless I had the choke all the way up.

    From everything I've researched, it seems like this could be a gummed up carb. My problem is that I don't know anything about engines. Is there a guide that I can follow to taking apart and cleaning the carb? Is this something that an amateur can take care of or do I need someone with small engine experience?

    I would really love to learn everything I can about this thing and fix the problems myself (especially because the local power equipment place has a month long backlog). I'm going to change the oil tonight and check the fuel line, replace the fuel filter and see if that makes any difference.

    Appreciate the help!
    First off I believe that service reminder works by run time only. It shouldn't have anything to do with the running problem. It's not like a "check engine or gauges" lights on a car.

    Second. How much grass are you cutting with your lawn mower? Distance like acres and how high like inches? Sounds like you are over heating this engine for some reason. I think that the maximum size lot JD recommends for your mower is 1.2 acres. (If I remember correctly) You should only be removing 1/3 of the total grass length in a single mowing. I had a 2005 L108 with a 42" deck. It was similar to your tractor. I used it to cut some overgrown grass like 2' high. It was all that thing had to get it down. Even creeping along the 2 blades left a Mohawk down the middle. Even cutting at the highest setting. I had to cut everything twice at least. Each cutting after that was a struggle because of all the dead grass laying on the new growth. Ended up buying a lawn sweeper to get it up.
    I'm going through something similar with a lot that I cut on the side. It was 2' high but my X540 was able to cut it without too much trouble. Yesterday's cutting is the second time. However that tractor chugged through it. I still need to use my lawn sweeper to get things back to normal.

    Change fuel, air, oil and filter are a good start along with plugs.

    Also check the intake for vacuum leaks. They will also make the engine run hot.
    Last edited by H-D dealer dude; 05-22-2017 at 07:26 PM.
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    Thanks for the reply. Our entire lot is 1.8 acres, 1.6 would probably be the max mowable area. The last time I went out there was some high grass, maybe a foot, but nothing crazy. That could explain the overheating, but even after running it for 5 minutes the muffler seems to get real hot. I'll check those things tonight.

    Thanks again!

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    Quote Originally Posted by ChickenMan View Post
    Thanks for the reply. Our entire lot is 1.8 acres, 1.6 would probably be the max mowable area. The last time I went out there was some high grass, maybe a foot, but nothing crazy. That could explain the overheating, but even after running it for 5 minutes the muffler seems to get real hot. I'll check those things tonight.

    Thanks again!
    The exhaust will get hot but usually not glowing. Maybe pick up an inferred temp gun too see what the actual temperature is.
    Plugged filters and old oil won't help it run any better. Definitely replace all of it. You can get a service kit from JD that includes everything you need.
    What you were doing with it is definitely putting a heavy load on the engine.

    Make sure that the transmission stays clean. Especially the top where the fan is. Blow it off at least after every use. Check it from time to time while you are mowing.

    Also use the leaf blower on the engine. Blow down through the round screen on top of the engine. That's the air cooling system for the engine. If it has grass plugged up inside it will also cause it to over heat.
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    I would guess a lean running engine. Having to choke it is an indication of not getting enough fuel for whatever reason.. Plugged jets in carb.. Clogged fuel lines of filter.

    Sent from my LGL52VL using Tapatalk
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    Thanks guys. Definitely going to do some work on it tonight, I have the maintenance kit so hopefully I can take care of it.

    Thanks again!

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    Quote Originally Posted by xcopterdoc View Post
    I would guess a lean running engine. Having to choke it is an indication of not getting enough fuel for whatever reason.. Plugged jets in carb.. Clogged fuel lines of filter.

    Sent from my LGL52VL using Tapatalk
    Another thing that wouldn't hert is checking for intake leaks. Before you put the air filter cover on. Spray some carb cleaner around the intake manifold with the engine idling. Mainly the outside of the carb, carb to intake and intake to cylinder heads. Also around any any vacuum lines. Just a little shot is all you need. If the cleaner gets sucked into the engine the speed will change. Avoid getting it into the carb opening. This will give you a false positive. Of course be careful because the cleaner is flammable.

    Another couple things to keep on the back burner.

    It's about time to give your engine a valve adjustment.

    Also changing your transmission fluid. However the unit must be removed from the tractor to do this.
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    Thanks! Wasn't able to look at it last night, hopefully can take care of this tonight.

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    Forgot to post back here, immediately after I changed the oil and air filters, blew some stuff out, the engine stopped surging (woooooooo!). Went back and changed the fuel filter just for good measure (the old one looked super old), and hopefully will have few problems going forward.

    Thanks again for all your help!!
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    Quote Originally Posted by ChickenMan View Post
    Forgot to post back here, immediately after I changed the oil and air filters, blew some stuff out, the engine stopped surging (woooooooo!). Went back and changed the fuel filter just for good measure (the old one looked super old), and hopefully will have few problems going forward.

    Thanks again for all your help!!

    Glad to hear that your problem was fixed. Just remember to clean off the old grass and dirt periodically.

    Also FYI never blow out an air filter. High pressure air blows holes into it. Then dirt can go right through. The foam per filter can be washed. I use BelRay foam filter cleaner and oil. You can use dish soap and motor oil but I don't recommend it. You only need enough oil to catch dirt. Never make it so wet that it soaks into the paper filter.
    Last edited by H-D dealer dude; 05-30-2017 at 03:57 PM.

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