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Mountfield sp414 (rs100 engine) only runs for a few seconds

Discussion in 'In the Garden' started by Stringman_uk, 22 Sep 2019.

  1. Stringman_uk

    Stringman_uk

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    Hi all
    I have a mountfield sp414
    it was working fine but then died in use. fiddling around i discovered the pipe from the tank to the carb was split.
    I replaced this primed the carb and it run for about 3 seconds. it would not catch when i pulled the starter cord.
    Primed it again and the same thing happened.
    So i deduce that there is no fuel getting to the carb unless its pumped by the primer.

    The fuel pipe is new so cant be that. An ideas what it could be?
    could it be an airlock in the carb?

    Thanks in advance
     
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  3. Burnerman

    Burnerman

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    The primer bulb on this engine actually shoots a sharp blast of air into the carburettor.....across the main jet actually which obligingly allows a couple of drops of fuel into the engine to help it start.
    These carbs dont air lock so its time to take the carb off, remove the float bowl and clean out both the needle jet controlled by the float and the main jet dead centre.
    Notice this carb should have two screws on the float bowl.....one secures it and the other is a drain off.
    When you take the float bowl off, check for rust in there.
    Im guessing this is quite a new machine, with the red primer on the top?
    John :)
     
  4. Stringman_uk

    Stringman_uk

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    Burnerman
    Thanks for the reply
    yes its about 3 years old with the red bulb.
    Interesting about what you said about the primer bulb- when i pushed it almost seemed to squirt fuel into the carb.
    I will take the carb off ( do i need to remove the whole thing or just the bowl? ) and have a look. is it compressed air to give it a clean?

    many thanks
     
  5. Burnerman

    Burnerman

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    With the carb in place, you should be able to remove the float bowl, then the float pin which will release the float and needle valve. Any grot in there should be displaced by allowing fuel to run through.
    Any more than that then its carb off Im afraid - and an aerosol of carb cleaner is great, even better if you have compressed air.
    Thankfully, the gaskets usually survive!
    John :)
     
  6. Stringman_uk

    Stringman_uk

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    Thank you so much
    I will give that a try when i am next home!!!
     
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  8. Burnerman

    Burnerman

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    Best of luck with it!
    On occasion, if its impossible to pull the carburettor back far enough for any reason to remove it, its acceptable to unscrew one of the studs.....depends on the design.
    John :)
     
  9. Stringman_uk

    Stringman_uk

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    Burnerman

    I managed to take the bowl off the carb and give it a good clean, looking up at the body there was a some white plastic on a sort of hinge and a hole going through the body that seemed to have a small rod with a hole in the middle. this had a slot cut into it ( i presume for a screwdriver) but it wouldn't budge.
    i cleaned it all and blew through it. all seemed fine. the only aerosol i had was wd40 so i gave a squirt of that and cleaned it again.
    put it back together and it works fine.
    thank you so much for all your help
     
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  10. Burnerman

    Burnerman

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    Most welcome!
    With the float bowl off, the float itself is revealed and it is hinged there courtesy of a steel pin. With the pin pushed out, the float falls free and brings the float needle with it......this device allows fuel to run from the tank into the carb.
    In the carb centre, surrounded by the float is the main jet and the emulsion tube above it - this can be unscrewed for cleaning should the need arise, but only with the carb removed from the engine.
    John :)
     
  11. Stringman_uk

    Stringman_uk

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    Resurrecting this thread as seem to have a new problem of a similar issue. I have noticed that the mower has a fuel leak somewhere as when I finish cutting the grass it has fuel in the tank, when i next get it out the tank is empty. When I used the mower last week the mower ran fine for a while ( about 20 min) then cut out. It would turn over, catch for a few seconds then die. Now I have the same old problem where it will run for a few seconds then die.
    I have seen a replacement carb on ali express for a £10 and think its worth trying that as a first call.
    Any thoughts?
     
  12. Burnerman

    Burnerman

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    For sure, a replacement carb is a good thing to have - at least it should give you time to fiddle with the original one if you want to.
    Fuel leaks aren't always visible as the fuel can sometimes drain directly into the engine, if the float needle valve is passing slightly. This can result in a too high oil level and chuffs of black smoke when starting up. Having a fuel tap solves that one, of course!
    Please make sure your fuel is clean - I get many issues with folks using rusty steel cans but they won't be told, of course!
    John :)
     
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