Sym jet 4 50cc won't start

Discussion in 'The Workshop' started by Tony h, Oct 20, 2020.

  1. Tony h

    Tony h New Member

    Messages:
    8
    Hi all new to all this .have just bought a sym 4 was running but now will not start think it may be the carb but to be honest I am more at home to cars than bikes but wanted to give it a whirl lol.
    So bought the jet 4 18 plate misfires on way home but bearable engine management light flashing 5 times then off dont know if that means anything but runs OK no drop in power ect but day later won't start have checked the kill switch not that turns over has spark bypassed the filter cleaned plug tried to kick start all failed think may be the carb can't find any thing on cards any body know about this bikes thanks in advance 1
     
  2. MARSH

    MARSH Whooooo!

    Messages:
    3,200
    Rides:
    Piaggio Typhoon
    It must be EFI ? If it is you'r not going to do much with it . If you do cars this will be easy, S.O.H.C Check valve clearance 0.004 in, 0.005 ex.
     
  3. Tony h

    Tony h New Member

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    8
    Will the bike have a fule pump if so where is it ? Can't find in the tank when turning over fule seems to splutter out the stops . Efi unit or carb ?
     
  4. Stevep

    Stevep Well-Known Member

    Messages:
    5,895
    Pictures please of the carb/throttle body/bike in general would help
    If you have a spark but non start, is the plug getting wet or staying dry?
    Dry is no fuel to the cylinder, wet is compression test time.
     
  5. Tony h

    Tony h New Member

    Messages:
    8
    Hi thanks for the reply Steve p
    Have finally attached a pic.
    Have taken plug out again there was a slight wif of fuel but plug didn't feel wet or look wet .
    The bike is
    Sym jet 4 50cc 2018
     

    Attached Files:

  6. Tony h

    Tony h New Member

    Messages:
    8
    Would it have spark if efi ?
     
  7. Stevep

    Stevep Well-Known Member

    Messages:
    5,895
    Ok, that's a carb.
    Take the fuel pipe off the carb and put the end in a clean jar.
    On the manifold is a vacuum pipe. Take that off the manifold and suck on it.
    Fuel should flow out of the fuel pipe while you are sucking and stop when you stop.
    This will test the vacuum tap on the tank is working as it should.
    No flow on sucking says the tap is knackered.
    If that checks out ok, do a compression test next. It's the quickest way to rule out the condition of the piston and bore.
    Compression should be upwards of 120psi.
    Check for a spark at the plug by grounding against the cylinder or other earth point, frame, stud etc.
    If that's ok, then whip the carb off, strip it, and if possible ultrasonic clean it.
     
  8. Tony h

    Tony h New Member

    Messages:
    8
    Well thanks for that Steve p
    Have now ruled out the tap tested as suggested that was OK . Have spark so not that while waiting for compression tester to arrive striped the carb gave it a good clean fule getting to carb just out of thinking left the front of the carb open at front while turning over there was no fuel at the exit port ether spray or residue can't really decide whether the plug is getting wet but faint smell of fuel but not overly wet . How we should the plug be ? Thanks
     
  9. Stevep

    Stevep Well-Known Member

    Messages:
    5,895
    Carb has to be on the manifold in order for it to get fuel sucked through.
    Has the compression tester turned up yet?
     
  10. Tony h

    Tony h New Member

    Messages:
    8
    Hi just done compression test and retested between 75 and 90 have now got fuel down to the carb but not to the plug .
     
  11. Stevep

    Stevep Well-Known Member

    Messages:
    5,895
    That's below where it needs to be. The reading should be, as a minimum, 100psi, preferably over 120psi.
     
  12. Tony h

    Tony h New Member

    Messages:
    8
    Well it's taken a time but finally got some parts new piston new seal's new carb bits missing from old .
    So my question now not wanting to sound like a nump how do you get the correct valve clearance as the contract with the top of the valve seems to fit inside a small dip any body got a guide for this ? Or any one done this ?
     
  13. Stevep

    Stevep Well-Known Member

    Messages:
    5,895
    It looks a bit fiddly when the head is on, but it can be done; you can set the valve clearance with the head off the engine, just remember to get the cam in the right place for when you fit it.
     

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