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    Lawnmower starts but doesn't stay on.

    Asked Apr 1, 2008, 07:32 PM 12 Answers
    I have a MTD 4.5 HP Briggs and Stratton push mower. I've emptied the gas tank and put fresh gas in it. I changed the oil. I replaced the spark plug and air filter with new ones. I also removed the fuel bowl and cleaned it out. The lawn mower starts but won't stay on. I did find that if I pull the string and it starts, I can keep it on by pressing the prime bulb over and over. As soon as a I stop pressing it, it stops. I guess I can have my buddy sit on top of the mower pressing the prime bulb while I attempt to mow my lawn but that would look rather silly. Help!

    Last edited by elcastle; Apr 1, 2008 at 08:18 PM.
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    KISS's Avatar
    KISS Posts: 12,505, Reputation: 838
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    #2

    Apr 1, 2008, 08:41 PM
    I can't tell if you have a float or diaphram carb, but most likely the fuel valve in the carb is stuck because you stored it with old gas in it. You must either allow all the fuel to run out or use Stabil, a fuel additive when gas is to be stored for longer than about 2 months.

    The only way to clean a carb is to take it apart. Clean it and put it back together. Sorry.
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    elcastle's Avatar
    elcastle Posts: 11, Reputation: 1
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    #3

    Apr 1, 2008, 08:47 PM
    When I removed the fuel bowl I did notice that there was a small float similar to what you see on an automotive fuel pump. What should I use to clean the carb? If I take it apart, do I need to watch out for springs or other compressed items popping out? Thanks
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    KISS's Avatar
    KISS Posts: 12,505, Reputation: 838
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    #4

    Apr 1, 2008, 09:03 PM
    A hole in the float causes flooding and your not having that problem.

    The float operates a valve that lets fuel into the bowl. Hopefully the bowl was full of gas when you removed it.

    The fuel gets sucked up into the carb by the vacuum created by the piston. The mixture screws. There is usually two. One for low speed and one for high. Usually they are set by bottoming them and then backing out 2.5-3 turns. Then try to start engine and adjust until the engine runs smooth at low and high speed. The smaller one, I think is low.

    Spray carb cleaner works fine. Incidentally spray carb cleaner can be used like starting fluid and should be for small engines.

    The diagrams of briggs engines are on Home - Briggs & Stratton.

    The carb may have 10-15 parts. Nothing should go flying, but have a clean surface to work with. A re-build kit might cost about $10.00. No instructions. If the engine is old, it might be worth considering.

    Did you leave old fuel in the tank or bowl?
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    4ndr3w5's Avatar
    4ndr3w5 Posts: 14, Reputation: 0
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    #5

    Apr 1, 2008, 09:08 PM
    Quote Originally Posted by elcastle
    I have a MTD 4.5 HP Briggs and Stratton push mower. I've emptied the gas tank and put fresh gas in it. I changed the oil. I replaced the spark plug and air filter with new ones. I also removed the fuel bowl and cleaned it out. The lawn mower starts but won't stay on. I did find that if I pull the string and it starts, I can keep it on by pressing the prime bulb over and over. As soon as a I stop pressing it, it stops. I guess I can have my buddy sit on top of the mower pressing the prime bulb while I attempt to mow my lawn but that would look rather silly. Help!
    Well, my dads did the same thing.

    IF you have even 1 SMALL LITTLE GRAIN OF DIRT IN THE CARBORATOR, it will do that.
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    MOWERMAN2468's Avatar
    MOWERMAN2468 Posts: 3,214, Reputation: 243
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    #6

    Apr 2, 2008, 05:06 AM
    Quote Originally Posted by 4ndr3w5
    Well, my dads did the same thing.

    IF you have even 1 SMALL LITTLE GRAIN OF DIRT IN THE CARBORATOR, it will do that.

    So true, so true, MICROSCOPIC particles can cause major carb problems.

    Also, check the primer bulb for cracks, and the housing.
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    elcastle's Avatar
    elcastle Posts: 11, Reputation: 1
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    #7

    Apr 2, 2008, 10:17 AM
    I bought the mower in 06/2003. Not that old but not no where new either. The bowl did have fuel in it but it also had some grayish sludge built up on the bottom. I did dump out all of the fuel from the tank and bowl (including grayish sludge). I will remove the tank now and flush it out with some carb cleaner. Haven't checked the prime bulb or housing but will. Wish me luck as I venture into rebuilding my carburetor. I will keep you posted as to the outcome hopefully with pics for others with the similar problem to see.
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    SkipB's Avatar
    SkipB Posts: 41, Reputation: 2
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    #8

    Apr 2, 2008, 01:13 PM
    If the mower is a 2003, more than likely there arn no adjustments on it other than idle speed. When you take off the bowl nut from the bottom of the bowl, make sure it it thoroughly clean. There is a small metering hole in the side of the threads, it controls the amount of fuel entering the main jet. If it is plugged and they usually are from sitting it will not allow fuel to the carb. Locate it and clean it out with a small piece of wire and then flush it with carb clean.
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    MOWERMAN2468's Avatar
    MOWERMAN2468 Posts: 3,214, Reputation: 243
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    #9

    Apr 2, 2008, 03:54 PM
    Hope it works out elcastle.
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    elcastle's Avatar
    elcastle Posts: 11, Reputation: 1
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    #10

    Apr 2, 2008, 07:56 PM
    As MOWERMAN2468 suggested, I removed the carb and cleaned it out as best I could with carb cleaner (didn't actually rebuild it). Also cleaned out all three holes on the screw that holds the fuel bowl in place with a fine needle and carb cleaner as SkipB stated. Put it all together, primed it, gave it a yank and it stayed on! I shut it off and tried it again with great success. Mowed my lawn today with no problem what so ever. Thanks to all who replied to my dilemma. You guys are awesome!! Hope this helps someone else as well as it did me.
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