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Honda Spada random misfire

Discussion in 'Technical and Troubleshooting Torque' started by ChuppaChup, Feb 19, 2010.

  1. Hi all,

    I have a weird symptom that started 2 days ago with my spada.

    It's an 89 model, 65000kms which all looks original.

    After 15 minutes, with light or heavy throttle, the engine misfires like it loses complete spark for a second or two, the tacho also drops to 0 at this point. It does this 4 or 5 times, then cuts out clean.

    If the bike is left to stand for 30 seconds or more, it will fire up as if nothings happened. Then be happy and revvy for another 5 minutes or so and do it all over again.

    What I've done:

    This first happenned wednesday night (scared the cr4p out of me) . I thought it may have been dodgy fuel, so last night i pulled the carbs out and gave them a good clean, there was a little varnishing in the bores (probably from it sitting still prior to me purchasing it) but nothing that stood out as a definite answer.
    Once reassembled, I put in fresh fuel (standard unleaded, not ethanol blend or premium) fired it up and it ran really well,very responsive, no flat spots (there was a tiny one right as I cracked the throttle open before cleaning the carbs).
    I also gave the plugs a good clean when I bought it (a week ago) as they fouled because i didn't really know how much choke to apply.
    I've checked the electrical connections going to the CDI box under the seat, all fuses, relays, they are all sturdy and clean.

    What I will check tonight:

    I've got a copy of the Spada manual and will check coil winding resistances, magneto resistances and spark plug wire integrity.
    At this stage I've ruled out a fuel delivery issue, because when it runs, it runs really, really well. But with these random misfiring which can happen at any time (it ran for close to an hour after the 3rd time it cut out in the space of 15 minutes) I'm thinking electrical.

    I'm picking up fresh plugs tonight (local repco has them) NGK CR8EH-9
    The symptoms seemed to be of a less extent if I pushed the plug wires in really tight (but they didn't have much play anyways).

    Would these symptoms be the ingition unit dying, magneto dying or a shorted spark plug?
    It feels like then you hit the ground button on a whipper snipper and it starts cutting out, then when you release it it fires back up. The tacho falling to zero certainly indicates this. I'll check the ignition circuit for any grounded wires.

    Any other suggestions would be greatly appreciated.


  2. I suggest you contact Caringbah Motorcycles,

    53-55 Captain Cook Drive
    Caringbah, NSW 2229
    Tel 02 9524 6456

    If they don't know how to fix a Spada problem, no-one does :LOL:
  3. Petrol tank vent
  4. I'd be on the lookout for an earthing problem. As you said, you've eliminated most possible causes of fuelling causing the issue, so chances are it's electrical.

    With 20 year old wiring, I wouldn't be surprised if something had worked loose, and was making intermittent contact - that explains the tacho dropping out at the same time, too.
  5. Sorry I only had time for a quick read and post before.

    Can you explain the above a bit better? when you release what?

    How loaded is the engine when it happens?

    It could be a crack in a plug, a lead or a plug cap. Spray some water about the leads and plugs whilst it's running.

    Replace the plugs regardless.

    Have you checked spark viibly with a plug out of the bike?

    Check/clean both battery terminals.
  7. OK that tells you something. Both leads?

    Now repeat with your actual plugs and see if it is the same.

    If the spark isn't as strong you know it's the plug/s themselves.

    btw never run too long with an odd plug in a lead. The difference in resistance can bugger coils and cdi.
  8. Update...

    I've checked all the wiring and it checks out fine, I puled the coils out while changing the spark plugs and measured the primary coil windings, cyl 2 (front) measured weird, intermitently measuring fine, the high resistance or oven open circuit.

    But when it was on the bike the primary resistance measured fine at the cdi unit. Another weird thing is, it still sparks, but it appears that it's sparking out of time. With a timing light that's been busted for 4 years, I'm at a loss as to how it still sparks when it measures bad.

    Either way I'll ring Caringbah Motorcycles tomorrow for a replacement. Hopefully that will fix it. Would it be necessary to replace both coils or could i get away with just the one?
  9. Hey mate.

    Did you end up fixing this? Find out what the problem was? Sounds like I'm having very similar problems to you :-s
  10. Are the leads the right way round?
  11. Bad coil was my problem. It was breaking down under load.
    In the end it also took out a transistor in the CDI unit, which required replacement (along with a capacitor and a diode in there).

    To look at your coil winding resistance take a multimeter, put it on ohms scale and measure between the two prongs were the wires go in, they should read between 2.8-3.2 ohms. Then put the multimeter in the highest ohm scale you have (10-20Megohms usually) and touch between the prongs, body of the coil (where the bolt goes through) and where the spark plug wire screws into (yeah it screws in), these should be on infinity scale (the needle shouldn't move, like an open circuit).

    A replacement coil cost around the $50 mark (used) while a CDI unit, the cheapest quote i got was at Warwick Farm Recyclers and it comes in at $160 (hence why i took the cheaper option of opening it and replaceing components).

    Good luck with it all, I hope your fix is not a difficult one.
  12. Take any photos? A "how too" on that would be a handy thing.
  13. Good bit of troubleshooting there!
  14. Sorry i didn't take pictures, it was a case of open it up, check the part number on the transistors and that they forward votlage how they should (by using a multimeter, check resistance one way it should be high, the other way it should be lower).

    I found this page extremely useful http://www.jetav8r.com/Vision/IgnitionFAQ.html.
    There's a slight difference in the Honda CDI over the Vision one (component placement, etc). But basically they are the same for these early bikes (except the Honda one has hot melt glue all over the components... fun).

    What i found was that one transistor (the front one) was getting really hot and discharging constantly, so the coil was just sparking as soon as there was enough voltage to jump the gap in the spark plug (not using the dwell curve supplied by the timing chip).

    The transistors I used came from Wagner Electronics and were $12 or $16 each (don't remember i think they were $12). Before I soldered them back in, I plugged the unit in without them and checked the voltages at the pins, the faulty transistor had an unusually high (supposed to be 5v but was sitting at 12v) forward bias which meant the input 5v circuit had failed (faulty cap/resistor bridge), so I got lucky there.

    If i couldn't get to the failed components I would have just gone to the wreckers and got another unit (I'm not that electronically capable), but my uncle was a chip level electronics tech (my late father was an engineer, I'm the dropout) and he gave me pointers in between drinks one evening.

    If i couldn't find a cdi unit under $200 I would have just used a megasquirt for the timing only. But this would have needed a working bike for me to take a timing mark off (I would have pleaded here if i could borrow one).

    I have a V3 version of the megasquirt on the Mx5 (turbocharged) that is running fine, but for the bike the earlier board would do the same thing.