Electrical Help please.

Discussion in 'Motorcycle Technical Discussion' started by James Caldwell, Sep 5, 2004.

  1. Having decided to get back into dirt bike riding after a 10 year lay-off
    (married, mortgage, house, kids.... etc) I pulled my old XR250 out of the
    shed.

    Trouble is I can't start it. It used to start from cold after about 6
    kicks, and first kick when hot.

    Checked the obvious: I've cleaned out the carb, put new gas in, the is heaps
    of compression, valves are not stuck.

    There is a spark but it's not the brightest. Had the local bike test the
    coil. They say that's OK. There isn't an audible click like you get with a
    really
    good spark.

    I don't want to start swapping parts as that gets a bit expensive if I guess
    wrong.

    I'd appreciate advise on the following:-

    - Is there a way to determine (measure) if the spark is bright enough?
    - Does anyone have any diagnostic tests for mags and black boxes?

    If I have to start swapping, I'd start with the black box. Question is, do
    I <have> to buy a genuine Honda one (which I believe are expensive) or is
    the a generic accessory part that I can use?

    James

    jamesatracingdrivesdotcom
     
    James Caldwell, Sep 5, 2004
    #1
    1. Advertisements

  2. James Caldwell

    bob prohaska Guest

    Very true; my tlr200 starts and runs reliably, but the spark
    is inaudible and invisble in normal daylight. The bike _is_
    relatively sensitive to an over-rich mixture, and it's doesn't
    take much to flood it.

    It can be hard to distinguish too much from too little fuel. One
    easy test would be turn off the fuel, drain the carb and try a
    bit of starting fluid. If the bike fires you have spark, if not
    there's a good cause to suspect ignition trouble.

    hth,

    bob prohaska
     
    bob prohaska, Sep 5, 2004
    #2
    1. Advertisements

  3. I've tried starter fluid. Not even a hint of firing.
     
    James Caldwell, Sep 5, 2004
    #3
  4. I've been really careful to clean them all out.



    James
     
    James Caldwell, Sep 5, 2004
    #4
  5. Makes no difference. It's not only the jets that give the problem. It's
    also all the horrible little galleries, nooks, crannies and so in inside
    the carb.

    This is a real problem with modern unleaded fuel, which has all sorts of
    additives and stuff. The volatiles evalporate, leaving a horrible mess.
    After 10 years of standing, I'd expect:

    a) To have to get the carb ultrasonially cleaned or

    b) Throw the carb away.

    Seriously. In the last two or three years I've had to jettison carbs on
    at least three old bikes I've been resurrecting and source decent
    known-to-be-functional replacements (in one case, a brand new carb).
     
    The Older Gentleman, Sep 5, 2004
    #5
  6. <Snip>

    It's the carb.
     
    The Older Gentleman, Sep 5, 2004
    #6
  7. James Caldwell

    bob prohaska Guest

    Hmm, that's a bit discouraging, but possibly not decisive.

    Starting fluid can't help if the mix is already too rich.
    Did you drain the carb first? If so then I'd begin to suspect
    the ignition.

    bob prohaska
     
    bob prohaska, Sep 6, 2004
    #7
  8. James Caldwell

    pragmatist Guest

    I'd agree in suspecting mixture problems, but I'd also check any
    rubber 'boots` or gaskets in the airway for leaks. If that checks
    out, I'd try spraying the passages in the carb body with 'gunk` or
    brake cleaner, and then soaking it in a closed jar of raw gas for
    a day or two in the hope of dissolving out any accumulated varnish.
    There's no guarantee, but it has been known to work.
    Best of luck,
    Pragmatist - "R75/5 forever!"
     
    pragmatist, Sep 6, 2004
    #8
  9. James Caldwell

    pragmatist Guest

    P.S. To previous post:
    If there's a vacuum fuel cock, check the vacuum line!
    I once spent an interesting afternoon trying to diagnose a
    friends no starting problem that turned out to be caused by
    air leaking into the carb from a cracked vacuum line.
    Pragmatist
     
    pragmatist, Sep 6, 2004
    #9

  10. Good advice. As was the other post.
     
    The Older Gentleman, Sep 6, 2004
    #10
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.