got a bad one here

Discussion in 'Motorized Bicycle Trouble Shooting' started by crassius, Sep 19, 2016.

  1. crassius

    crassius Well-Known Member

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    a while back I had a guy with bike that sat several months - wouldn't start

    decided motor full of fuel and got it started with lots of smoking, but it had sat so long with fuel in it that it took over 20miles to get it up to full speed and even then it was weak uphill - assumed gas had evaporated from fuel in motor to leave gummy mess down there that would slowly clear up over time, and it did after a few months

    now I have one worse - got it started and fuel was so dried out inside that I get no smoke, and it needs half throttle to idle, but finally catches on and over-revs

    checked everything else (seals, gaskets) - replaced muffler carb CDI Intake manifold spark plug just in case - good compression at 125lb

    hoping that if I can keep it running it might clear up, but wonder if I'm missing something

    never seen one this bad

    any ideas of something I might have missed?
     
  2. Slogger

    Slogger Member

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    I'm going with a mondo air leak at the case split.
    Filled with gas and left to sit for months maybe the gasket has gone away between the case halves.
    I'd check the torque on all the case bolts. If they seem loose that would be a clue.
    That's all I got.. It is weird.
    Good luck, Mr Crass!
     
  3. crassius

    crassius Well-Known Member

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    hit them all with impact driver a couple days ago (even the three under the clutch) - yesterday I taped a white paper towel to bottom of motor in case gasket had a gap in it that tightening wouldn't fix - came out clean

    beginning to think "it's dead Jim"
     
  4. Slogger

    Slogger Member

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    ??????????
     
  5. curtisfox

    curtisfox Active Member

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    Have you tried sea-foam in the gas, it really helps to desalted the varnish and crud.........Curt
     
  6. crassius

    crassius Well-Known Member

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    no, didn't try that - had a day of DR apts, then a day of rain - will try to get it going again today, then maybe just give up on that motor
     
  7. bairdco

    bairdco a guy who makes cool bikes

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    Have you taken it apart? Piston top and head might be carbonized, rings might be stuck, etc.

    Every old motor I've had, I'll pull the top end and clean it up, replace the gaskets, and rewire it before I even try to start it.
     
  8. crassius

    crassius Well-Known Member

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    it was a new motor half a year ago before it sat - did look inside and all looked good (tho very wet).

    One difficulty with a repair shop is to keep from charging more for labor than a new part would cost.
     
  9. crassius

    crassius Well-Known Member

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    got another POS like above

    same thing in that everything looks good & good compression, but it sat for many months

    ran so weak I could barely keep it running 3 or 4 times a day for a couple days, and now is starting to get a bit smoother with more power

    been thinking evaporated fuel in bottom of these leaving tarry substance in bottom that interferes with new fuel, but cleaned motor very well to see if any residue shows up outside where case gasket or base gasket may have deteriorated from sitting dry

    still clean so far, but I'll post if it turns out that these gaskets fail from sitting
     
  10. Agreen

    Agreen Member

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  11. crassius

    crassius Well-Known Member

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    yeah, I use a water spray as it is also good for cooling while running on the bench

    I though about the base gasket even tho is wasn't seeping oil because when cooling the motor, I seemed to get a slight reaction when spraying down there.

    not enough to be sure something was bad, but it is very clean now and I'll see if anything shows up - motor keeps getting smoother as it runs tho, so maybe a dried out gasket will re-wet itself after running enough and seal OK again

    I'd like to figure this out as this is now second one after sitting 6 to 8 months.
     
  12. sbest

    sbest Member

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    A couple plates to block off the intake and exhaust, one with a Schrader valve and the other with a nipple to a low pressure gauge will answer a lot of questions about case leaks. I pump it up to 5psi and see how long it holds and where it leaks.

    I was just burned by a tank filter plugged up with gummed up evaporated fuel.
    It would leak enough fuel to run for a bit and then die.
    There was always fuel in the carb when I got it back to the shop. Finally I check line flow.

    Steve
     
  13. crassius

    crassius Well-Known Member

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    true, I've never bothered to set up for leakdown testing, as keeping cost below what a new motor would cost is the usual goal - anything more than 2 hours labor is half the cost of new motor with no more problems
     
  14. sbest

    sbest Member

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    Things always seem to start out simple and then go sideways.
    When they go sideways, a leakdown test is a good place to start on a worn motor.
    2 plates on, a couple pumps with a bicycle pump and check for leaks.
    10 min tops, learn so much.

    The KTM and Blaster engines are much more complicated, especially to install and remove. I usually leak test them before installation of even a new motor.

    Steve
     
  15. crassius

    crassius Well-Known Member

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    fortunately, I've only seen 2 like this in all the years and many hundreds of bikes - if I determine that it is base gasket, then I can lift up top end and put non-hardening permatex there for a nice $10 fix - if it is tarry residue in bottom of case, then it's run it till it clears or new motor
     

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