bike wont start gilera 125.help please :)

Discussion in 'The Workshop' started by SPRunnerSP, Jun 14, 2014.

  1. SPRunnerSP

    SPRunnerSP Member

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    yeah ive done a compression test it had over slightly over 100 psi, the spark maybe isnt good enough?? il re charge battery also and get a new spark plug, ive took the carb off this after noon to clean it
     
  2. SPRunnerSP

    SPRunnerSP Member

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    69
    i only put the top end on when i first started this post, and did a compression test and was geting over 100psi, just tryed to do one now and cant get the tester to screw into the top end proppa and kicked it over and was only geting 50 psi, but when i put my fingers over where the tester screws in air is passing down the sides so this is why its showing as low im guessing, and i did what you said coverd the carb and kicked it , nothing still, its quite hard to kick a bike with no center stand while covering the carb with ya hand lol but i have no doubts in the top end tho. cos i just put a lil petrol down the spark plug hole and put spark plug back on and it kicked over but then just cut straight out
     
  3. ReverendSkipper

    ReverendSkipper Member

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    Hi there Merlin and OP - a newbie on the forum here and I'm not trying to tread on any toes or anything, just as someone who used to work for many years with electronic ignition systems I thought it may be helpful to know that CDI type ignition works a bit differently, and will give different results than a standard 12v induction setup when tested as suggested - with CDI the (primary) coil winding resistance is much lower - usually 1/2 Ohm or less compared to 2 or 3 Ohms for the 'traditional' setup,

    - and the coil is designed to spark when power is applied to it by the CDI circuit rather than (via field collapse) when it is disconnected - CDI stands for 'capacitor discharge ignition' - a capacitor in the electronics is charged to a few hundred volts by the electronics, then at the firing timing that voltage is rapidly discharged as a short pulse through the very low resistance coil winding giving an almost immediate spark - hitting this kind of coil with just 12 volts won't replicate the spark intensity of a working CDI and can actually damage a working CDI coil due to the high current flow for an extended period.

    Hope that helps a bit but as you said these coils are cheap enough and I just got a replacement for my Skipper just because I wasn't sure of the condition of the old coil despite tests seeming to show it was OK.


    Cheers folks, and be well.

    Shaun.
     
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  4. Merlin

    Merlin Old School Biker

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    2,305
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    2007 TKR WRC 50
    Thanks, Shaun. This Gilera is being a royal pain in the arse for this guy, so feel free to jump into the thread if you think you can help out.

    A lot of my experience is with pre-80s bikes and is prior to the introduction of CDI ignition systems, so I may tend to default to tests that I would have done back then to troubleshoot a bike.

    The OP reckoned his coil was shot, so a brief test using 12v for a very short duration to see if it did spark at all was worth it and proved that his coil was defective.
     
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  5. ReverendSkipper

    ReverendSkipper Member

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    If I can think of anything I'll jump in, but my experience is also rather limited, hence my own struggles with the Skipper!

    My experience mostly comes from what used to be our family business (Newtronic Systems Ltd, formerly 'Piranha') which went under some 8-ish years ago - we made (non-CDI/Standard induction type) electronic ignition systems to replace points on older vehicles and classics, as well as replacement reg.rec. units for bikes etc. - don't have much knowledge of CDI systems outside of what I already posted, and my diagnostics are maybe a bit rusty as well heheheh...

    Cheers Merlin,

    Shaun.
     
  6. Stevep

    Stevep Well-Known Member

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    5,895
    I had a Piranha ignition system on my old Goldwing a few years back. Think i may still have the ignition box somewhere.
     
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  7. SPRunnerSP

    SPRunnerSP Member

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    69
    Ok so have i now damaged my new coil with me putting the 12 v to it.... ??? cos bike still wont start
     
  8. ReverendSkipper

    ReverendSkipper Member

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    PiaggioSkipperST125
    When you said ''80's bikes'' I thought you might have at least come across one ',;~}~
     
  9. ReverendSkipper

    ReverendSkipper Member

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    PiaggioSkipperST125

    I'd say that's unlikely - brand new/healthy coil and a quick test like you did it should be OK.

    Is it firing at all/trying to start (the odd pop/engine firing sound), or is it just turning over and over?

    After trying to start it for a while (minute or so), is the plug looking 'wet' when you take it out? - By this I don't mean drenched, just damp/less than fully bone dry? - Plug needs to have been thoroughly cleaned and dried etc. before trying or you won't be able to tell.

    Wet plug = fuel but no ignition.

    Totally bone dry plug = no fuel and ignition 'likely' OK.

    As far as checking the coil the test with the plug out of the engine but earthed and connected to HT lead, turn engine over and look for sparks test like you did before is what I'd suggest - if you have regular sharp sparks ('tick-tick-tick-tick-tick' etc.) then coil and CDI unit are both pretty much working.

    There are scenarios outside of these parameters but Sherlock tells us start with the likeliest things first and eliminate them, before exploring the less likely/more absurd ',;~}~

    Cheers!


    Shaun.
     
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  10. SPRunnerSP

    SPRunnerSP Member

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    69
    thanks shaun yes its doing the odd pop engine firing sound , when i took out the plug yesterday it seemed dry wasn't wet, so i put a bit of petrol down the spark plug hole even tho i no its not a great idea , an put spark plug back in, kicked it over and it fired/pops for a sec or two then just cut out. and if i spray starting spray into carb and give few kicks it does ops pop and fire but thats about it, im getting fuel to the carb and i also cleaned the carb out. when i did the coil test i only hace a kick start so i could see a spark wasn't a big spark looked small but blue dont no how visible the spark is meant to be....also ive changed the coil and the cdi over the last 2 weeks... when i put this top end on about 2 months ago i did compression test and was getting over 100psi but now cos engines in bike its hard to screw the tester in the top end cos the angle and space so it will not screw all the way in so when i did a recent test it only came back 50psi but im sure this is due to it not screwing in as its at an angle so air is escaping from the sides.
     
  11. Merlin

    Merlin Old School Biker

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    2,305
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    2007 TKR WRC 50
    Have you had the stator cover off at all? One thought that has occurred to me is ignition timing or possibly the clearance between the ignition pickup and the rotor. If the clearance isn't correct or the pickup's position has been adjusted incorrectly, you might have starting issues (right spark, wrong time).
     
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  12. SPRunnerSP

    SPRunnerSP Member

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    69
    no ive not well i need to get a flywheel remover??
     
  13. ReverendSkipper

    ReverendSkipper Member

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    PiaggioSkipperST125
    I'd just had a thought since you'd changed the cylinder head - was the valve timing out with the valve chain/belt - but then I realised yours is a 2 stroke lol!

    But this lead me to wonder about the reed valve block on the intake - is that all set properly and fastened up with no leaks?

    And then this lead me to - vacuum hoses to the manifold - are any such hoses in place and if so are they connected well? Are the hoses intact/are there any splits/holes/leaks? (take both ends off, block one end off well with a wet finger (seals better!) and suck hard on the other using your mouth (not lungs - if you see what I mean?), sealing the vacuum in with the end of your tongue - you should be able too feel with your tongue if any vacuum is being lost.

    Do you have a separate 2 stroke oil feed to the intake manifold or carb, or do you run pre-mix? If there's a feed is it connected properly? Any leaks in the oil hose? If you are running pre-mix oil and petrol in your tank, have you properly blocked off the oil intake into the manifold/carb?

    Also, was the scoot running well before you changed the cylinder head?..

    Also (and I know this may sound silly, but) - did you remove and refit the piston when you changed the heads over? If so, is the piston in the right way round? I don't mean upside down lol I mean front-to-back- if the intake side is facing the exhaust port and vice-versa, well that'd cause problems!

    You have new CDI and coil, but do you have new HT lead, spark plug cap and spark plug?..

    - Just trying to cover everything I can think of mate...

    Cheers!

    Shaun.
     
  14. SPRunnerSP

    SPRunnerSP Member

    Messages:
    69
    hi thanks for the reply shaun , ye i got cdi coil and ht lead and cap all fresh and new plug. im useing the standard dellorto phvb20.5 carb , but iam now premixing and ive not blocked the oil intake on the carb. and before i put this top end on, i had a pm 172 on it and it drove for about 2 miles and then started back fireing alot and then refused to start. so i took that top end off and put on my old 125 back on what was working fine all in good condition. and yes piston was put in the right way. and ive not checked the vacuum pipes, i will do that tho, but im geting fuel to the carb so im sure the vaccum is working
     
  15. ReverendSkipper

    ReverendSkipper Member

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    "and ive not blocked the oil intake on the carb... " ? - If this is not blocked off, it needs to be blocked off or it'll draw air in where it isn't wanted.

    Apart from that can't think of anything else just yet bud...

    Shaun.
     
  16. ReverendSkipper

    ReverendSkipper Member

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    PiaggioSkipperST125
    Hey SP any progress/luck yet mate?..


    Shaun.
     
  17. Merlin

    Merlin Old School Biker

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    2,305
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    2007 TKR WRC 50
    Shaun's right. Block that oil intake off with a short length of hose folder over and secured with a cable tie, to make it air tight.
     
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  18. SPRunnerSP

    SPRunnerSP Member

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    69
    still no joy i feel like putting a match to it :(
     
  19. Merlin

    Merlin Old School Biker

    Messages:
    2,305
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    2007 TKR WRC 50
    Where do you live? There might be a member on here that's not too far away that could take a look at it.
     
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  20. SPRunnerSP

    SPRunnerSP Member

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    69
    i live in north london islington
     

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