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  1. #1

    Join Date
    Apr 2013
    Location
    Framingham, MA
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    99

    Intermittent spark at low rpm/throttle load?

    I have had a miss that has plagued me for a while. It happens at low throttle taking off and at idle periodically, but the bike revs out to 10,500rpm just fine. I think I have narrowed down the miss though, but not sure what the culprit really is. While doing a bunch of work yesterday (throttle cable, new points/condenser, fixed leaking float, reset, resynched carbs), I noticed that when the miss happened, the timing light cut out completely or at least halved its sparking frequency or worse. This also happens on deaccell, but deaccell isn't really an issue so far. The coils are original, but with the wires replaced with MSD wire, 5k ohm caps and new plugs. As far as I can tell, nothing should be causing this miss. Is this possibly the old coils finally starting to show their age?
    1970 Honda CB350K2 - Daily rider (Wife's bike)
    1978 Yamaha XS650SE (in rebuild, holed piston)
    ------
    CB350 HID mod: http://bit.ly/14Vohw1
    CB350 Project log: http://bit.ly/103aafO

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  3. #2
    Super Moderator Mydlyfkryzis's Avatar
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    Jul 2012
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    Northern NJ USA
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    3,824

    Re: Intermittent spark at low rpm/throttle load?

    How were the wires replaced? The original were epoxied in....Did you epoxy the new ones in?

    Also, low RPM miss can be a low battery issue. At low RPM's (below 3000) the voltage drops because the alternator does not make that much current. You start running on the battery. If the battery is low, you will get a low RPM miss.
    Richard

    Mydlyfkryzis = Mid Life Crisis
    My Build: http://www.hondatwins.net/forum/view...hp?f=5&t=16466
    ______________________
    1991 Honda Nighthawk 750 "Big Red"
    1976 CB360t "Sophie"

  4. #3

    Join Date
    Apr 2013
    Location
    Framingham, MA
    Posts
    99

    Re: Intermittent spark at low rpm/throttle load?

    Wires were replaced by leaving a tail of the original stranded wire and used crimp connectors to couple the cores together, then insulated the connection. I used the called for 5ohm caps and b8es plugs.

    I have an led volt gauge to add to the tach gauge similar to the gauge restoration thread, but it isn't in yet. As far as I can tell, charging system is working well enough, no dead battery, no lack of power for electric starts etc. I will have to put a DVOM and see if there's a voltage drop associated with the miss...
    1970 Honda CB350K2 - Daily rider (Wife's bike)
    1978 Yamaha XS650SE (in rebuild, holed piston)
    ------
    CB350 HID mod: http://bit.ly/14Vohw1
    CB350 Project log: http://bit.ly/103aafO

  5. #4
    Super Moderator Mydlyfkryzis's Avatar
    Join Date
    Jul 2012
    Location
    Northern NJ USA
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    3,824

    Re: Intermittent spark at low rpm/throttle load?

    I did the voltmeter in the tach too...comes in handy...
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    Richard

    Mydlyfkryzis = Mid Life Crisis
    My Build: http://www.hondatwins.net/forum/view...hp?f=5&t=16466
    ______________________
    1991 Honda Nighthawk 750 "Big Red"
    1976 CB360t "Sophie"

  6. #5

    Join Date
    Apr 2013
    Location
    Framingham, MA
    Posts
    99

    Re: Intermittent spark at low rpm/throttle load?

    of course, I post about the bike's spark issues and it decides to run like new the whole way in to work today. Maybe it just wanted attention...
    1970 Honda CB350K2 - Daily rider (Wife's bike)
    1978 Yamaha XS650SE (in rebuild, holed piston)
    ------
    CB350 HID mod: http://bit.ly/14Vohw1
    CB350 Project log: http://bit.ly/103aafO

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