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Thread: another bike won't start query

  1. #1
    Join Date
    27th April 2020 - 14:56
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    1997 honda cg125
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    another bike won't start query

    i was amazed to see people still use forums to be quite honest. super stoked though.
    well a little back ground. i found a 1982 honda cg 125 in my uncles hay shed and seeing more and more of these cafe racer builds thought F why not? its my first road bike and after stripping powder coating various parts and the frame, putting it back together with some new parts and electricals(new second hand stator). i got the bloody thing running after about 2 weeks of tinkering one of the issues was a broken ignition coil which wasn't grounding luckily a cable ties holding that together for the mean time.....
    so after about a week of riding this thing up and down the road and it not missing a beat (definitely needed some adjustment though something was causing it to be under powered) i went on an OE for about a year and now it won't start??
    things ive tried and things to help?
    it has new 98 fuel in it.
    spark plugs new and appears to have a strong spark when grounded on engine.
    ignition timing and the contacts seem to be aligned properly.
    kick start and i believe these run with out the battery and the battery is just for accessories ?
    it backfires sometimes and have had steam/smoke come back out the air intake.
    when it does fire it will only do a put, put then nothing.
    have tried various choke positions and throttle positions
    have rebuilt and cleaned the carby which has new seals
    no kill switch, key is on, fuel is on

  2. #2
    Join Date
    1st March 2017 - 06:23
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    1976 Honda GL1000, plus implements
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    If it pops sometimes then you’ve obviously got spark, kill switch on, etc, so that’s ok.
    You’ve cleaned carb so it’s not just stale fuel. But I’d still be looking at fuel delivery. Did you clean the carb properly? The jets are really tiny and block easily and often need more than just a squirt of carb cleaner. Did you reassemble the carb properly? Check fuel filter? Make sure the air cleaner isn’t full of mason bees?
    Actually I’m a fan of using a bit of ether at this point...
    High miles, engine knock, rusty chrome, worn pegs...
    Brakes as new

  3. #3
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    27th April 2020 - 14:56
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    that was a quick reply i'm impressed!
    ill take another look at the carb. redo it in a cleaner environment and check those jets more carefully. i honestly don't think thats the case though. i am going to order a new spark plug AGAIN, i'm concerned it may have flooded and gotten wet and that could be producing a weak spark and not quite enough UMPH! even so i thought it would at least start nd just run like a bag of D's
    lets assume that doesn't work? is this a shop job?

  4. #4
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    28th January 2015 - 16:17
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    It's sounding more like a shop job, if the bike's worth that.

    I'd guess it's likeliest to be an old battery which has finally died. They really don't like being left for a year (assuming that nobody has been tendering it for you). I'm not 100% sure if the battery is essential on this bike but it'll certainly help when starting.

    You mention a strong spark when plug grounded... out of the engine isn't the same as inside it. You need more HT voltage to create a spark when it's dealing with a compressed mixture - have a look for Paschen's Law, this deals with this phenomenon.

    The second possibility is the coil, assuming it's still the one held together with a cable tie (you don't mention replacing this). Cable ties relax a bit over time and it might not be tight enough any more. The coil might also have degraded further. On that note, HT leads don't last forever and if the insulation on the lead has broken down then you'll lose spark voltage.

    Third possibility: reg-reg got hit with a voltage spike when the original stator died and isn't working properly any more. A total loss system (I.e. running off battery charge only) will still work just fine while the battery holds up but as soon as the battery is flat, that's it, no go. You should see 12 V static on a healthy battery with the bike not running, 11 V is the bottom limit before permanent battery damage with the ignition switched on, and 13-ish to a maximum of 14.5 with the engine running and revving, if the charging system is still working OK.

    Fourth possibility: bad ignition switch, bad grounds to frame, or rotten wiring in the loom, particularly the crimp joint connectors to battery and coil. The bike's from 1982, that's nearly 40 years, and I've recently found that even crimp joints relax and corrode internally given enough time. If the copper conductors leading into the crimp are brown with oxide then the joint's suspect, if the copper has gone green then that's it, it's stuffed. Cutting back wiring and replacing terminals is possible but gets very fiddly very fast, if a replacement loom can be purchased at an acceptable price then that's usually a better way to go.

    So... (just my guesses) could be battery, could be coil, could be rec-reg, could be loom/switch/grounds, could be any or all of them. As Honest Andy has mentioned, being sure that the carb jets are clear will also help, blast through with compressed air will be good but don't use wire, too easy to drill / file them bigger.
    Last edited by OddDuck; 28th April 2020 at 08:39. Reason: revision

  5. #5
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    27th April 2020 - 14:56
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    Quote Originally Posted by OddDuck View Post
    It's sounding more like a shop job, if the bike's worth that.

    I'd guess it's likeliest to be an old battery which has finally died. They really don't like being left for a year (assuming that nobody has been tendering it for you). I'm not 100% sure if the battery is essential on this bike but it'll certainly help when starting.

    You mention a strong spark when plug grounded... out of the engine isn't the same as inside it. You need more HT voltage to create a spark when it's dealing with a compressed mixture - have a look for Paschen's Law, this deals with this phenomenon.

    The second possibility is the coil, assuming it's still the one held together with a cable tie (you don't mention replacing this). Cable ties relax a bit over time and it might not be tight enough any more. The coil might also have degraded further. On that note, HT leads don't last forever and if the insulation on the lead has broken down then you'll lose spark voltage.

    Third possibility: reg-reg got hit with a voltage spike when the original stator died and isn't working properly any more. A total loss system (I.e. running off battery charge only) will still work just fine while the battery holds up but as soon as the battery is flat, that's it, no go. You should see 12 V static on a healthy battery with the bike not running, 11 V is the bottom limit before permanent battery damage with the ignition switched on, and 13-ish to a maximum of 14.5 with the engine running and revving, if the charging system is still working OK.

    Fourth possibility: bad ignition switch, bad grounds to frame, or rotten wiring in the loom, particularly the crimp joint connectors to battery and coil. The bike's from 1982, that's nearly 40 years, and I've recently found that even crimp joints relax and corrode internally given enough time. If the copper conductors leading into the crimp are brown with oxide then the joint's suspect, if the copper has gone green then that's it, it's stuffed. Cutting back wiring and replacing terminals is possible but gets very fiddly very fast, if a replacement loom can be purchased at an acceptable price then that's usually a better way to go.

    So... (just my guesses) could be battery, could be coil, could be rec-reg, could be loom/switch/grounds, could be any or all of them. As Honest Andy has mentioned, being sure that the carb jets are clear will also help, blast through with compressed air will be good but don't use wire, too easy to drill / file them bigger.

    great break down thank you! so basically the sparks not good enough? ill check that battery then ill start with a new coil and HT line. im assuming these should be pretty universal. have all the wiring terminal tools and gear so relocating it if needed isn't an issue. see how that goes for a start.

  6. #6
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    27th April 2020 - 14:56
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    i replaced the spark plug again and gave it a few kicks this arvo first kick was a back fire then gave it another 6 ish kicks which resulted in a few fires then a pop with white smoke coming back out the air intake. what could this mean?
    im also struggling to find a 6 volt coil attached is the oem one, searching those number on it had no result. maybe a local bike store?
    still haven't tested the volts
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  7. #7
    Join Date
    28th January 2015 - 16:17
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    Test the volts.

    Seriously.

    Giving it a punt without measuring what you're doing is simply wasting your time.

    Another suggestion: take a very good look at the inside of the plug boot and see if you can see any black marks running in lines - it'll look like a broad pencil mark. If so then you're losing spark to carbon shorts. Sand them off and you're good to go again. Same goes for any sort of discolouration or dirt inside that boot.

    Also something I missed - ignition coil resistances, you'll need a multimeter for this, there'll be values for primary and secondary (HT) coil resistances. With 6V coils, yes, bike shop is definitely the way to go.

    White smoke coming back out of the intake is another sign of a weak ignition.

  8. #8
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    Does the plug lead detach from the coil? ie can it be wound out(unscrewed) ? if so what is the condition of the lead where is screws in? My bike had a problem some time ago where it would start, run ok then die a random time afterward. The coil wire was corroded internally to green powder. New piece of HT lead fixed it
    it's not a bad thing till you throw a KLR into the mix.
    those cheap ass bitches can do anything with ductape.
    (PostalDave on ADVrider)

  9. #9
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    19th October 2005 - 20:32
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    Quote Originally Posted by smithy96 View Post
    i replaced the spark plug again and gave it a few kicks this arvo first kick was a back fire then gave it another 6 ish kicks which resulted in a few fires then a pop with white smoke coming back out the air intake. what could this mean?
    im also struggling to find a 6 volt coil attached is the oem one, searching those number on it had no result. maybe a local bike store?
    still haven't tested the volts
    Timing is out 180 deg

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