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non starting mower

Discussion in 'In the Garden' started by jfg, 13 Mar 2019.

  1. lostinthelight

    lostinthelight

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    Do you know the coil is duff or are you doing diagnosis by substitution?
     
  2. lostinthelight

    lostinthelight

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  3. Burnerman

    Burnerman

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    The coil is actually an igniter unit so measurements may not be that useful, however Ive tested a Briggs coil that I believe to be good....
    Cut out wire terminal to earth = 55 ohms
    H.T. Cap to cut out terminal = 2.6k ohms.
    Have you tried looking for a spark in the darkness? Can’t beat that one!
    John :)
     
  4. jfg

    jfg

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    Update on the wretched machine.

    I've fitted a new coil and spark plug. I now have much better spark than before. The carb has been stripped and cleaned, everything is clear. The float action has been checked and it works fine.

    Still it won't start with or without the cut out wire connected. I've tried easy start, nothing, I've tried a dash of petrol into the piston chamber & nothing. I've cooked the end of the spark plug on the gas ring to heat it up & still nothing.

    I did open the valve cover but all that shows is that the valves do indeed move up down. Without removing the head i can't examine the valves.

    Here is the only difference between old and new spark plug when fitted.

    The old spark plug is soaking wet and the small bowl around the electrode fills with petrol (flooding)

    The new spark plug does not.

    Finally i had one backfire which blew a flame flash back out of the carb (the air filter is put aside while testing)

    Where next? Head removal and valve check?
     
  5. Burnerman

    Burnerman

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    Just regarding the flooding, whether the plug is new or not makes no difference there.
    Kicking back through the carb is due to either a weak mixture or - as LITL’s original suggestion- the ignition timing.
    The timing is set, as you know - but its time to double check the flywheel woodruff key again. Sorry!
    Mark its position with paint on the crankshaft and flywheel - and see if the mark shifts at any time.
    John :)
     
  6. jfg

    jfg

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    I've been all over the flywheel and woodruff key, there is no movement in it at all.
     
  7. jfg

    jfg

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    Part of me wonders if the kill switch is constantly engaged (even though it physically operates ok) but then i guess it would not spark?
     
  8. lostinthelight

    lostinthelight

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    You said in an earlier post the key was loose in the keyway?
    What I suggest doing is remove the flywheel and tripple check there isnt a mark on it, it may even be the wrong one if previous owner had been trying to get it going...key that is.
    If key is perfect, drop flywheel back with keyways aligned. Slide the key in,jam the blade, then turn fw anticlock until it jams and tighten the fw nut keeping the fw the anti clock position.
    What this does when the key is not a good fit is ****** the timing a little.
    A picture of the key would be good?
    I hope you tried one of the suggestions for checking the spark under compresion before splashing out on a new coil?
     
  9. Burnerman

    Burnerman

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    If the flywheel key has sheared at some time, theres always a bit of scoring on the crankshaft and flywheel tapers.....if you are happy with that, then so be it.
    I dont suspect ignition failure, you seem to have dealt with that - including trying to disconnect with the kill switch wire disconnected. If you are getting a spark, and have tried another plug, then thats ok too.
    I still suspect flooding. Does your engine have the red or orange primer bulb, which you are supposed to depress 3 times when the engine is cold? This shoots raw fuel out of the emulsion tube directly into the carb choke....a bit crude but it does work so long as you dont overdo it!
    Try starting with the air cleaner box completely off so as to bypass this function.
    Point of info - easystart is effective on diesels, not so on petrol engines!
    Do you think this engine has been in bits before, do you reckon?
    John :)
     
  10. lostinthelight

    lostinthelight

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    Carb cleaner works well though:)
     
  11. jfg

    jfg

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    yes i substituted easy start for carb cleaner.

    I'm going to check the blade and shaft with a manual turn tomorrow to see if there is any damage or shaft bent. The engine does not look to have been messed with. Lots of crud undisturbed over the bolts.

    The air filter was alsogunked right up, probably original filter!!!

    I will also revisit the flywheel and key.
     
  12. Burnerman

    Burnerman

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    Bent crankshafts are common enough - all it needs is the blade to clip some concrete :eek:
    However, it doesnt affect the starting but the machine shakes like hell.
    John :)
     
  13. jfg

    jfg

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    Another check of the flywheel with marks as suggested and there is no movement since i last reseated it.

    Could there be an issue with the magnets themselves??
     
  14. Burnerman

    Burnerman

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    I've never had an issue with a flywheel - usually there are two magnets in close proximity, and there are 'keepers' so the magnets can retain their - er - magnetism.
    You said you have stripped the carb down - how happy are you with the reassembly there? Some Briggs motors (can't say about yours particularly) have a red rubber seal where the needle valve gets pushed in to when the float lifts, and its dead easy to lose. :eek:
    With the air filter off, so you can see down the carb choke.....can you see raw fuel at all?
    Any chance of trying a replacement carburettor?
    John :)
     
  15. lostinthelight

    lostinthelight

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    I have started stood machines with empty tank with a good squirt of carb cleaner into the inlet. so to eliminate an excess of fuel ,drain the fuel from the float chamber and either clamp the fuel pipe or drain tank . Then spray carb cleaner in to seeif it fires.
     
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