I think i have a pretty unique problem but I'm not sure

Discussion in '2-Stroke Engines' started by christulio, Jul 7, 2010.

  1. christulio

    christulio New Member

    Hi everyone, I'm kinda new here but I've been lurking around for a couple months now and have loved the information and helpfulness of the members here. Anyway, i have an engine kit about a month old and still in the breakin period, but have recently run into a problem - the intensity of it i have not yet realized.

    Anyway, let me tell you how it happened. I was coasting along at a pretty decent clip when i noticed my engine started throttling funny. I stopped and it turned off and i checked my idle screw and noticed it was missing, but lucky me it was resting just below the carb on the engine, so i put it back and kept riding. A few minutes later my throttle starts bogging out on me and i can feel the engine slowing down to a stop, i look down and the idle screw is completely gone and i dont know for how long. The engine stops and i try pedaling to start it again, and it sounds like its about to start, but never does. A few seconds later i hear a loud pop kind of like a backfire sound (maybe it was my engine backfiring, im not sure). Now my engine just wont go. I think what it does is "turn-over" but thats it. Basically, it runs as long as im pedaling and twisting the throttle only makes it sound like its bogging out again and it stops altogether when i stop pedaling.

    I dont know if too much air got into the cylinder or what, im a pretty amateur mechanic so i dont even know if thats bad. But its been a whole day and ive tried everything to get it running again (checking the troubleshooting thread, to following all the advice ive read, etc), and it only feels like more problems are popping up.

    What i've done so far:
    -replaced the idle screw with another screw that seems to be doing the same job of holding the carb assembly up inside the carburetor
    -put a new mixture of gas into the tank with a lower oil to gas ratio to hopefully increase combustion
    -cleaned my carb air filter
    -checked my spark plug for a spark and found out there was NO spark (one of the problems that popped up) which seems weird to me because the engine was running perfectly for at least 15 minutes before it bogged out
    -as a result of that, i replaced the stock spark plug with a new ngk b6hs plug, still no spark and same problems (i'm starting to think im testing the spark plug wrong, if someone could give me very specific instructions on how to see if it's sparking thatd be great)
    -checked the magneto to see if the connections are good
    -disconnected my killswitch in case it was shorting out
    -adjusted my clutch in case it wasnt fully engaging
    -tightened every nut and screw i could find, including the head bolts and carb intake and exhaust manifold

    i dont think the engine is just ****, because it's been riding well for about a month and this is the only problem i've had. i hope somebody can help me out here.

    thanks everyone!

  2. GearNut

    GearNut Active Member

    Check for spark by removing the spark plug and resting it on the cylinder head. Be sure that the metal hex portion of the spark plug is touching the metal of the cylinder head. Keep the spark plug connected to the spark plug wire.
    Lift the rear wheel off the ground and turn the engine over by turning the bicycle cranks.
    Some folks have to tape the spark plug in place and ride the bike around while watching the spark plug for signs of life. This is easiest to do at night time.
    As for what exactly the problem is, I am not sure yet.
    Do you have any intake leaks?
    While the idle speed screw was gone it created a large intake leak.
    Look down the spark plug hole with a flash light and inspect the top of the piston to be sure a hole did not get burned through it.
    Concerning the idle speed screw, there should be a small relatively strong spring that fits around it. The spring is compressed in between the screw head and carburetor body.
    The pressure created by the spring is supposed to prevent the screw from turning by itself caused by engine vibration.
  3. christulio

    christulio New Member

    GearNut, I just got back and did what you said, and now im sure there's no spark. do you think this could be a problem with the CDI? Magneto? Would it be easier to just buy those parts and replace them? I also checked the top of the piston and didnt see any hole, the piston looked pretty good IMO, it was still pretty silver and didnt seem thrashed or anything. I dont think i have any intake leaks. And about the idle screw, i guess the spring didnt do its job lol, but the screw i put in to replace it is pretty solid i think.

    Thanks for the quick reply!
  4. GearNut

    GearNut Active Member

    Is there a chance of water inside your mag housing?
    If you are using the stock wire connectors between the mag and CDI box get rid of them. They are JUNK! They can look good and still be bad.
    Solder together and seal the connections with heat shrink tubing or electrical tape. Heat shrink tubing is better than tape.

    It could also be the spark plug cap or wire has a bad connection.
    It is a good idea to replace them anyways with a good automotive one or an NGK one (it's a cap and wire assembly) purchased from one of the sponsoring vendors here.
    The cap unscrews from the wire, the wire unscrews out of the CDI unit.
    Both are notorious for problems.

    Try to correct known weak issues with the factory parts, and diagnose the parts you have before throwing more $ and parts at the engine.
    Nobody likes to buy new parts to replace perfectly good parts.
  5. Huntington

    Huntington Member

    The pop sound could be bad, Have you removed the head and inspected the piston, make sure you didn't blow that thing. if it did blow, fragments can be jamming the stroke, stopping the engine from turning and producing a spark.
  6. christulio

    christulio New Member

    Okay so i got new wires and everything like you said GearNut and I'm still stuck in the same spot - I can pedal and engage the engine, and it brrrs louder when i give it throttle, but theres definitely no power, and no push.

    I did notice something else though. Thick brown fluid was leaking from the exhaust and also from the head of the engine itself. I took off the head to check the gasket and the inside and everything seemed right, but who am i to say anythings right haha

    Basically the inside of the engine had the same brown fluid, probably combusted gasoline. it wasnt flooded, but there was a thin coating of it all over the entire inside. The gasket wasnt broken (which was what i first thought happened when i heard the pop). The piston looked fine, it wasnt broken to my knowledge, i dont know how to check it thoroughly though.

    any ideas?
  7. GearNut

    GearNut Active Member

    Check for spark, and if you don't get any, remove the spark plug wire from both the CDI unit and the spark plug boot. It unscrews from both. Twist the wire counter clockwise. It is held in place by threading onto a screw inside the Spark plug boot and CDI unit. Cut about 3/8" off of both ends and reassemble the wire assembly to the spark plug cap and CDI unit. If you can, just forgo the wire cutting process, ect. and replace the wire with a good automotive one that has a 90 degree boot on one end. The stock wires are JUNK!
  8. christulio

    christulio New Member

    GearNut, I did what you said, still no spark. I'm starting to lose hope!

    Is the brown fluid a bad thing? are there any other possible sources to the problem?
  9. GearNut

    GearNut Active Member

    The brown fluid should be no problem at all. I suspect that is just unburned fuel passing through the engine and picking up a bit of brown color on it's way out of the dirty innards of the muffler.

    You could have a bad CDI or a bad mag. There are tests for those that cost alot less than outright replacing them as a fill in test (called parts basketball).
    Try searching this site for the test procedures. They are here......somewhere.
    I will look too as time permits.
  10. Stan4d

    Stan4d New Member

  11. GearNut

    GearNut Active Member

    After reading the links below, I smacked my forehead. I never asked you yet, what are you doing with the white wire? It should be taped off, well insulated. (not connected to anything).
    Sometimes the obvious escapes me..... :eek:
    Here are some links that may help:
  12. Al.Fisherman

    Al.Fisherman Active Member

    Can be isolated..taped. I take mine off completely at the coil terminal. Output not good enough to run the engine and lights at the same time. It puts out about 7.5vac and minimal amps.
  13. core2kid

    core2kid Member

    I had the exact same problem like this. I left it overnight and the next day I choked it and pedaled for a couple hundred feet. The engine finally kicked in and I held the clutch, slowly moved the choke down and gave it a little gas. Since then, it's been running fine. What threw me off was that I never had to choke it and suddenly after about 100 miles, I had to choke it on the first start of the day.
  14. core2kid

    core2kid Member

    To be more accurate on my previous post, I was riding the first day and for about 50 miles, the engine ran fine. No priming/choking and it would start right up. Suddenly it wouldn't start like that. I thought the engine was dead (day before I had heard a click but the engine kept going). It would start but it would die as soon as I held the clutch. I tried everything, cleaning carb, removing air filter, cleaning fuel filter, removing fuel filter, cleaning the net in gas tank, priming it etc. Finally I thought of choking it. At first it struggled because of an overflow of fuel in the carb. I drained the carb in a cup, pushed the prime button about 10 times, choked (lever all the way up) and it started in about 100 feet. As soon as it started, I stopped and held the clutch and slowly moved the lever back down revving as I went until it was steady enough. I also had the idle screw almost all the way in so I knew that it was idling fast enough. After it started, I unscrewed the idle. Since then, I've put about 300 miles on the bike and it's still running like new. No engine mods, only mods I did were mounting screws replacement and head screw replacement was done according to the seller on eBay.
  15. christulio

    christulio New Member

    Hey guys thanks for all your help I'm definitely learning a lot about these engines. Problem is mine still doesnt work :confused:

    Ive done everything you guys have said - changed the wires, pedal while its choking it for 100 feet (actually went around the block a couple times, but still when i pull in the clutch the engine dies out), i even bought a new CDI hoping on the off chance that would fix it, but so far no egg.

    Im sorry to continue bothering you all, but if you think there could be any other problem please dont hesitate to say the first thing that pops in your head. im willing to try anything to fix this thing!

    but ****, if i cant fix it now im thinking of just scrapping the engine or selling it for whatever parts still work and saving up for a new one. Not having a bike for this long has really put a damper on my activity as that was pretty much my only mode of transportation.

    So if you all dont have any other ideas i guess its back to pedalling for me :(:(:(
  16. core2kid

    core2kid Member

    Did you try without the air filter?

    It starts but then when you give it gas, it stalls. If that's the case, it sounds like the engine isn't getting enough fuel. Try to remove the fuel filter temporarily and also check the net thing inside the fuel tank and make sure it's clean.
  17. thuginfc

    thuginfc Member

    well seeing as you have no spark id replace the magneto ive been through 3 on 1 engine and still on the same cdi i dont think the cdi really has anything to fail cause its epoxy sealed...

    once i lost a mag due to riding in rain. once it overheated ot something and the solder from the wires meltied into the coils and once was a blown crankcase seal.

    the blown seal sounds most similar to your deal it ran fine i heard something weird stopped started back up and it slowly bogged to a stop... new seal and new magneto and bam im in there again