Obvious air leak, not so obvious spot. (Anyone experienced this?)

Discussion in '2-Stroke Engines' started by S.O.G., Sep 1, 2010.

  1. S.O.G.

    S.O.G. New Member

    Hey guys, before I describe my issue I'd like to say that I've already searched the forum and stripped my engine looking for the problem.

    I had almost finished my ride to work, at the very end my motor started to loose power and slow down. This happened in the last 50 feet of my ride. I parked it and when I came back to ride home it wouldn't start. Instead of coming to life it stays in that stage where it hasn't kicked in fully and is still warming up (you should know exactly what I mean by that) and in addition to this it would occasionally make a loud "pop" sound. I can only assume this is an air leak.

    Last night I took it apart partially (intake, exhaust, head, cylinder) because I figured it was a gasket leak. I cleaned them and everything else, but none of them looked bad. The exhaust one was nasty and corroding but it seals fine and shouldn't be an issue. I put it back together and tested it with the same results. It wont fully kick in and pops loudly (with an air sound not a metal on metal sound).

    I will be fully stripping it today. I'm planning on replacing the gaskets with new ones (probably gonna cut my own). I don't really know what else I should do.

    It has 1000 miles on it, the cylinder is smooth (I can barely feel one gash in it with my fingernail, it doesn't catch on it) It ran almost perfectly up until this point.

    Anyone experienced this problem before? I've exhausted my knowledge and any help would be appreciated.

  2. GearNut

    GearNut Active Member

    Have you checked out the crankshaft seals?
    Also, a plugged up muffler can cause similar symptoms to what you are describing.
  3. S.O.G.

    S.O.G. New Member

    I did not break it down that far, Ill try that today. The muffler is fine, I blew air thru it and it wasn't clogged.

  4. HeadSmess

    HeadSmess Well-Known Member

    it actually sounds more ignition related.

    if youve done the old "key banger" driving through tunnels, youll know what i mean.

    check everything, then

    if you got new ignition gear handy... why havent you put it in yet?

    if not. buy it :)

    all a leaky exhaust gasket does is make squeaky noises and more backfiring on compression braking

    an inlet gasket will make it lean maybe hard to run, but it wont make popping noises... and would have to be majorly obvious to be the prob...
    Last edited: Sep 4, 2010
  5. Wisski

    Wisski New Member

    If that "warming up" sound you're NOT describing is like "WAAAAAAAAHHHHHH" when you're peddling to get it to start, then those POPS are your sparkplug sparking, irregularly. Which could mean your CDI or your generator coil is failing, or maybe your kill switch HAS failed, and is on rare occasion not killing your current, or you have an intermittent short to ground somewhere in your electrical system.

    Remove the kill switch from the circuit. See if it starts. If so, kill switch is borked, replace or rewire. If not, break out the multimeter and test resistance on the CDI, and gennie. There's a post in the sticky thread "Engine Won't Start - TROUBLESHOOTING GUIDE" that tells you how to test both CDI and your generator coil - its http://www.motoredbikes.com/showpost.php?p=251663&postcount=23. I'd start with coil, test it, write down numbers, try to run it, test again. resistances for the coil connections should be low - if you get wierd numbers in the megaohms, your coil is bad. If you get no resistance at all, you probably have a short in the wiring somewhere. The resistances for the CDI listed in that post aren't reliable - they vary with manufacturer, components used, and layout of the circuit. Just make sure nothings shorted or open. Make sure you've disconnected the CDI and Coil before you test them.

    If your coil is bad, open up the gennie compartment and try looking for the ground connection coming directly off the windings. It'll be a few wires coming out of the plastic holder. It could be top or bottom, or it could be on the other side (you may have to take the coil out completely...it's not too bad getting it back in, just try not to damage the magnet). Put one multimeter lead on the wire (GENTLY) where it comes out of the plastic holder, and the other lead on the screw holding the insulated black wire to the laminate. If this reads huge resistances, you'll need to re-solder that joint. I'd also reinforce it with some solid core copper wire with the insulation stripped off (it'll help hold the solder on should heat and vibration destroy the joint). If the resistances are fine, test between white and blue wires. If there are megaohms here, or wide open, then your coil must be replaced. If all of these resistances are in the hundreds of ohms range, then the problem is either the wires leading out of the gennie compartment, or the solder joint on the blue wire. This is easy to test - one lead on black wire screw, one lead on the other end of the black wire. should be open. for blue wire, test from the TAB that comes out of the holder (NOT the joint), and the other end of the wire. If its bad, re-solder that joint, and retest. If its still bad, the wire is bad, joint is fine.

    If the CDI is bad, all you can really do is feel the blue/black wires (they shouldn't feel like there's metal needles pressing up from inside indicating a stressed and broken wire), test resistance on the sparkplug wire, and make sure everything is screwed in (be careful on the plug wire where it connects to the CDI. it unscrews counter-clockwise, and my first CDI seemed to have some epoxy holding the wire in). Also look INSIDE the boot - make sure the locking cap hasn't broken out of its holder. If it HAS - you'll need to replace the boot, or just screw the wire onto the head directly until you can get a new boot. Also if you haven't removed the slip-in connectors on the wires, MAKE SURE THEY'RE TIGHT. clean them with a degreaser, bend the tabs in a bit. if it takes some work to get the connectors to click together, you've got a good connection.

    If everything is fine to this point, check for shorts around the frame, where wires come near exhaust or engine, looking for melted insulation and bare copper (your bike frame is grounded to the generator). if you capped off your white wire, make sure the cap is FULLY intact, and no wires are coming out. If you've used your white wire in your electrical system, check it FULLY, cause really the only thing left is a short somewhere to ground.

    Good luck!