OK, got gas, air, and spark, but engine still won't start....stumped

Discussion in 'Motorized Bicycle Trouble Shooting' started by mobicon, Sep 24, 2016.

  1. mobicon

    mobicon New Member

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    Got new replacement parts, checked them all with meter before installing, all tested good.

    Installed them, tested all the connections, and their operation on the bike, all appear working fine.

    Held plug against cylinder head and rolled bike, sparks fine.

    Even removed both muffler and air filter in case of some possible flow restrictions. While pedaling the bike trying to start it, hold my hand in front of the exhaust port on the cylinder, and good gassy mist is coming out of it. Engine sounds tight and solid, and has good back compression. Can see the gas in the clear tube going into the carburetor also.

    Try it with choke on, with choke off, dry it out and try it again.

    Nothing will make this engine start. I'm stumped. Can anyone help me?
    Thx
     
  2. crassius

    crassius Well-Known Member

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    on rare occasions CDI will give good spark at wrong timing - not too common these days tho

    usually for a no start, I just check for oil seepage around gaskets & seals, then check compression - if all looks good, I assume fuel in motor and just keep working to get a pop out of it (sometimes with a few drops of fuel in plug hole) - if it starts and smokes a whole lot, just keep it running till it blows it all out
     
  3. mobicon

    mobicon New Member

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    How would I check/reset the timing? My magneto magnet only goes on one way and is keyed to the shaft, and there are no adjustments anywhere on my CDI box.
     
  4. Agreen

    Agreen Member

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    The rotor magnet can go on 2 ways.

    Sometimes I have to dry out the spark plug if it's been getting soaked in fuel.
     
  5. crassius

    crassius Well-Known Member

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    I have a thread here somewhere about making a temporary timing mark you could use to test with a timing light, or you could try a diff CDI unit since the timing is done in there (assuming rotor hasn't been changed).

    Putting some gas in plug hole should at least get you a pop if timing is right tho.
     
    #5 crassius, Sep 25, 2016
    Last edited: Sep 26, 2016
  6. mobicon

    mobicon New Member

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    Thank you all for responding to my posts. Problem appears to be fixed, although I'm not sure what I did for it.

    In search of a clue, I rolled bike while spraying starter fluid into the open intake port and it made bike run, so I pulled the carb apart, inspected it, found nothing apparently wrong and then reassembled it.

    However, after reassembly, the bike ran fine briefly, but then picked up a very rough running problem - it started missing like it was only firing on every OTHER stroke, and lost a lot of power. This happened first at all ranges, but then briefly began to do semi-well at low RPMs but fall apart as I went faster (is this what they call 4 stroking?).

    I figured putting a few miles on the bike might clear the problem because it had been down for so long, but after several miles, no improvement. Then I happened to look down and notice that, apparently my pant leg had brushed the choke lever half way closed. After opening it, the bike ran perfectly with all the power I remember from before....until 500 yards later the motor quit altogether. Then after cursing, I noticed that my pant leg had then closed off my fuel valve.

    Fixing those stupid little events, now everything is running perfectly, and I hope for a long time now. Just goes to show, if you're riding and the motor goes bad, look for the stupid little things first.
     
  7. Agreen

    Agreen Member

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    haha, you can solve that problem with some properly fitting pants
     
  8. ih8thisbike

    ih8thisbike New Member

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    I'm having the same problem but it's not my pants leg should I wear shorts. lol. I'm ready to set this thing on fire. I've built a total of three bikes everything's worked great this one is giving me the most problems. the only difference is mine is worth leaking gas out of the air filter so I adjusted the floats the gas stop leaking bike was running and now it will not no matter what I have checked the fuel is getting all the way down to the float it does not seem like it's getting from the float to the motor though any suggestions?
     
  9. Springfieldscooter

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    I would check your float level.
     
  10. crassius

    crassius Well-Known Member

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    if the plug ain't wet, it's a carb problem
     
  11. Slogger

    Slogger Member

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    Agree.. either a low float, a blocked fuel inlet or a clogged main jet.
     

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