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Hard starting and poor running

After replacing the filter & plug, and adding fresh gas, my toro mower w/ a
6 hp Briggs engine just won't run well. At idle and at speed, load or no load, it constantly varies in rpm and starts v. hard. Never a problem until this year, so I'm stumped, especially since I see no idle adjusting screw on the carb.
Thanks in advance for any help or tips.


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  • creekfishr1 Sep 10, 2008

    Ty for your suggestion Benimur.
    I did try w/o the filter, and ran it at high rpm, but it still idles hi and lo and still runs hi and lo, as if the mixture needed adjusting, but of course, no mix. adjusting screw on this model. Starts hard even with starting fluid.

  • creekfishr1 Sep 10, 2008

    Thanks again, and I'll try that.
    Btw, it is a four stroke, so no oil mix.
    In this engine the choke is always closed, because of a small spring, but holes are put in the choke-plate to allow air in. At idle or at load, it revs up and down, but more so at idle. A strange setup I agree, but all in the name of emissions I suppose. It's always run great in the past, and started easily, but I'm thinking the new ethanol-laced gas and/or dirt may be the problem.

    Hope this helps!

  • Kenny Hunting
    Kenny Hunting Feb 20, 2009

    Hi i have exactly the same problem.
    i have changed both springs that are connected to the carby because they where stretched and old.
    It didn't fix the problem, instead now it only runs flat out.
    I'm only guessing but i think it might have something to do with the white thingy under the pull start cover.

  • corbinator19 Mar 14, 2009

    it starts up and idles up and down what could it be? the springs are fine


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The reason it surges is it's not getting enough gas, the gas is stale or has water in it. Unscrew the jet out of the bottom of the carburetor and clean it and allow the gas in the carb bowl to drain out. Refill with newly purchased gas and be aware that gas for small engines should not be kept more then 30-45 days. I work on these units for a living and 70% of what we see are fuel related issues.

Also, the choke should never be on all the time. If you have a primer on your motor, it's doubtful you would have a choke. Perhaps you are looking at the throttle plate.

Posted on Apr 23, 2009

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Try running the engine without the filter and check if the idle would smoothen, maybe a little high. If problem persist, then it would be fuel delivery problem. If the idle is constant (but high), then some sort of blockage on the air filter or a vacuum leak.

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards. Thank you for using FixYa.

Posted on Sep 10, 2008

  • Louie  Role
    Louie Role Sep 10, 2008

    Hi again,

    Appreciate the reply/postback.

    A query pls, two stroke or 4 stroke?

    Alternately, you can try choking the carb throat, that is momentarily covering (with your palm) the opening where the airfilter base sits on. In effect, you are covering the air intake and forcing the engine vacuum to draw air elsewhere. The idea is to force any foreign object, dust, sand, grime, dirt, gum, sludge through whatever opening it can pass through and enter the combustion chamber.

    Alternately, if it were a two stroke engine, then perhaps too much 2T oil is inside the intake manifold and/or combustion chamber making the burning irregular. In some extreme cases, 2T could very well be also inside the crankcase and in a 2stroke engine, this would cause very lean mix.


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