Bought a second hand engine/bike, having some problems

Discussion in 'Motorized Bicycle General Discussion' started by Mind_Reader7, Jul 31, 2015.

  1. Mind_Reader7

    Mind_Reader7 New Member

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    Howdy folks, long time no post :)

    Over the course of the past few years I've had my shed broken into and heaps of my stuff stolen including my motorised bicycle (not that I was using it much anyway).

    I found a "hardly used" bike and engine posted in my local area and picked it up for $100. The front motor mount wasn't attached, the rear sprocket was installed wrong, no killswitch wired, fuel line leaked. I got it home, rewired the CDI using heatshrink and stuff, replaced fuel line and filter, fixed all the issues, and went to run it. It was bogging down, hard to start, a combination of problems. I noticed one of the head bolts were loose, the stud was stripped. I went to undo the other 3 bolts, each one just snapped the stud with no force. So I went and bought some 6mm threaded rod and replaced them all. Anyway, so far I've spent about $15 replacing parts on this bike, so no biggie really, but it's still running weird.

    Symptoms:
    Seems to idle ok, when I ride it, it jerks a lot, backfires, or just bogs down and dies.

    Tried:
    Disassembled the carb, cleaned it all, I adjusted the float, and the c clip.

    The float seems to kind of sometimes overflow, which I will fix soon, and when I adjusted the C clip, it ran normal for a while, then after letting it cool and running it again, it started bogging down and stuff again. I'm under the theory it's kind of flooding. Pretty sure it's not the head.

    I'm going out soon to pick up some O rings (inside the carb/manifold). I think air is getting in between the carb and manifold and a new spark plug (stock plug in there, will replace with NGK B6HS).

    Any other suggestions? I'm going to replace the spark plug, adjust the float again, add an O ring to the carb/manifold, then play with the C clip again.
     
  2. Mind_Reader7

    Mind_Reader7 New Member

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    It immediately runs a lot better with the new plug and some O rings.

    It runs great when the c clip is adjust to the very bottom (lean), but kind of cuts out at the highest RPM, where as anything above that seems to bog down and lose power.

    Any input?
     
  3. Davezilla

    Davezilla New Member

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    Can you see which main jet is installed? it's possible the previous owner put a bigger main in thinking it'll go faster.. Usually there's a number stamped somewhere on the jet telling it's size, you can also look at the jet opening to see is it looks like it was soldered and drilled or just drilled.

    Check that the jet is mounted securely and not just sitting on there finger tight, check the needle and seat valve for any small debris that could keep it from shuting off. Also check the intake for leaks at the intake gasket, this can cause some intermittant issues if the intake gasket is leaking.

    If everything else looks ok then check the base gasket, the case split line gasket, and finally, the crank seals, you can check these areas by running the engine at idle and spraying carb cleaner along these gasket areas and listen for any changes in the engine (reving up, slowing down, or dying) as the spray hits the gasket mating areas, if there's any change iin the engine that's where the leak is. You can chack the crank seals the same way but need to remove both covers then spray behind the mag rotor and the bevel gear while the engine is running, there should be no change with the engine unless you got a leak.
     
  4. Mind_Reader7

    Mind_Reader7 New Member

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    Well so far I've noticed this engine is pretty poor quality compared to what I've owned before, so I wouldn't be surprised by a leaking gasket, and I'll test for that I get a chance.

    As for the jet size, I actually did disassemble the carbon for general cleaning, and the jet is clear. I did however notice it was a lot smaller that what I remember. A very small opening. I was going to drill it a fraction bigger, but my drill press won't hold such a small drill piece.

    I'll keep you updated :)
     
  5. Trey

    Trey $50 Cruiser

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    For this task, Lord Vader Moderator once suggested micro drill parts and pieces from gun shows or shops.
    Maybe you can find something like that, even on the WWW.
     
  6. Springfieldscooter

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    The lower the c clip, the richer your mixture up to mid throttle anyways.
    The higher the c-clip, the leaner your mixture up to mid throttle.

    How does it run wide open?
     
  7. Springfieldscooter

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    I believe I would install the clip on the 2nd notch from top, and install a richer main jet.
     
  8. Davezilla

    Davezilla New Member

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    I got a set of micro drill bits and a pin vise from widgetsupply.com, If I remember right the main jet size should be soldered shut and re drilled with a #70 to 73 bit for best performance. The drill bit sizing system is the higher the number the smaller the bit, you can also find out a jet size when it's not stamped on the jet by using the micro drill bits to see which one pushes thru with just a slight resistance. You can use jet size pins if you got them, but the drill bits work the same way to quickly determine the jet's size before drilling.

    Personally I wouldn't re drill a jet or change it unless you nkow the previous owner was messing with the jets, the stock jet in these is usually on the rich side which is safe, but can make the engine a bit sluggish, if it's really boggy it could be running lean from a dirty carb or an air leak. It could also be a loss of compression from a bad head gasket or head nuts that came loose. Getting an old engine that's been sitting for some time can have all kinds of problems from something simple like the carb being gummed from fuel that's just sat in there for a few months or longer to blown gaskets or seals that'll let air sneak in or it could have gunked up fuel inside the case or even porosity caused by corrosion if it's been sitting a really long time...
     
  9. Mind_Reader7

    Mind_Reader7 New Member

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    Well after playing with the c clip some more, I found a pretty good place for it. I was still missing power at WOT (backfiring, losing power). The exhaust nut was loose (end wasn't on, loss of pressure) and my spark plug wasn't actually very tight. Seems to run pretty good now :)

    However, while I was doing the spark plug, I pulled the boot off and the spring fell out somewhere along the line :(

    Can I just buy any old spark lead and screw it on?
     
  10. Springfieldscooter

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    Yes you can! NGK sells a nice one and is probably available at your local auto parts store!
     
  11. Davezilla

    Davezilla New Member

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    Simple answer is Yes... and I prefer to use an automotive type boot and terminal, you will need that little screw on cap for the end of your spark plug but you can get one off a used spark plug or just buy another plug and dont take it off.
    This is Far more reliable than the factory plastic boot that comes apart.

    Also, a loose spark plug will cause some of the poor performance you've been experiencing
     

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