Engine Trouble Bogging engine, little throttle reponse

Discussion in '2-Stroke Engines' started by SchwinnAlloySeven_GT5, May 22, 2007.

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  1. Prologue
    Well, I was out on a ride the other day,and all of a sudden there was a *pop* and the motor started decelerating. I hit the clutch and look down and my sparkplug is missing! Must have gotten loose and quickly unscrewed itself. I stop and backtrack and it's nowhere to be seen!

    "That puppy must be in lower-level orbit" I think to myself. No biggie, I always carry a spare. However, upon installation, I find that the plug wire boot won't snap on! Seems that the plug had eloped with the contacts from the inside of the boot :shock:

    5 miles from home, but this time that North wind is pushing me. Next day, I locate a new wire from the local motorcycle shop , install it, and all seems well...

    My Grubee GT5 starts quickly and idles well, like it always has. But now, when I try to accelerate, all I hear is bog. With no load, it will bog, too. The throttle does not respond very well and the motor seems to "4-cycle" at any RPM but idle. The motor acccelerates very slowly when you goose the throttle off idle, too.

    I've checked all connections and bolts, tried another plug, another wire, different gas, all 4 settings on the Dax carb it's using, and the only time I noted a difference was on the lowermost setting. IIRC, that is the richest setting possible, and it ran slightly quieter at lower RPM - over 4000 RPM and it was worse. I put it back to the second setting.

    Now the odd part: If I take the time to accelerate over 32MPH, the engine has power again and quits "4-cycling". What in thunder is going on? Carb? Magneto? CDI?

    Please guys, I need help :(

  2. gone_fishin

    gone_fishin Guest

    if it was running fine before the fiasco & you've replaced plug and wire, then changing carb settings is probably not the solution?

    have you checked the exhaust for obstructions? intake air-leak? either of these could (possibly?) have occurred during the "pop"...just a guess, trying to help.
  3. The intake and exhaust gaskets seem to be fine. I have noticed an increasing bit of oil buildup around the exhaust baffle, though. I've always ran this motor at 20:1, which seems to be too rich according to many people's posts in this forum. This bog has always been there to a degree, but it is much worse now.

    I have a spare magneto and a CNS carb. However, I am very confused by the new carb, so I haven't put it on yet. There are 4 vacuum ports on it and none of them have lines on them. No instructions came with the carb so I have no idea how it should be configured. :???:
  4. azbill

    azbill Active Member

    I believe the vac ports are left open...just connect fuel line and mount choke lever
  5. thatsdax

    thatsdax Guest

    Better hope that...........

    A lose plug allows fresh air into the motor. This causes a lean condition and can damage a motor. I hope that has not happened to your motor. Always check intake bolts, spark plugs, ect for tightness. Intake fresh Air leaks are devastating for a 2 stroke motor.
  6. gone_fishin

    gone_fishin Guest

    which leads us (me, anyway) to "what kind of damage?"

    scored cylinder, wasted rings, that sorta stuff? and how long does the lean condition have to exist to cause damage?
  7. I've always checked bolts and plug before a ride. The day this happened, I had gone nearly 50 miles. Also, once RPMs are over 4000-4500, it will run normal with normal throttle response. It just takes 10 full seconds for the motor to finally rev that high! Now and then the motor will backfire or cut completely out, too. I do not have a kill switch.

    Swapped out magneto - no change. Ordered a CDI just in case. CNS carb is on, but it got too dark to complete the setup. Those open vacuum ports worry me! I'll be testing it out tomorrow.
  8. Finished up the CNS carb setup. Motor fired right up and has a little better response, but top end is gone and the exhaust smokes now. No amount of adjustment will fix it. Runs best with both screws turned all the way in. What a PITA :(
  9. Guest

    Guest Guest

    Broken ring?
  10. BikeHacker

    BikeHacker Guest

    I didnt read all of the responses so excuse me if i repeat anything. YOU HAD A MAJOR TIMING MALFUNCTION and the force of your piston meeting the explosion head on popped your plug. This could have killed you if the barrel had exploded like large dirt bikes do when they severely over rev. (70mph jumps) Pull your mag cover and look to see if your mag rotor has shifted or loosened on the crank. If so just knock it back on with an impact gun and your good. I put a mag rotor on backward once and it made that same detonation you mentioned.....
  11. No, and you should find whatever you bumped your head on and unbump it!

    I'm thinking it may be so. I put the new CDI on today and no change. The problem has to be internal. I have a spare set of rings, but I don't have a jug gasket :mad:

    Still out of commission for now :(
  12. gone_fishin

    gone_fishin Guest

    you don't need one, use RTV high temp alone, put it on the underside of the jug for a cleaner job.

    i have 200+ miles of trouble free service with this (thatsdax recommended) method & it looks like it's gonna keep holding :)
  13. Well, I pulled apart the jug for nothing, it seems. There is nothing wrong with the rings, everything looks fine. There is no scoring on the cylinder walls and piston is relatively carbon-free. I don't have a clue what the problem is.

    This bike is my main transportation and since it's been down, I've had to go back to 4 wheels and the gas money that goes with it. Any engine gurus with more ideas? :(
  14. Guest

    Guest Guest

    Is there something physically blocking the intake/carb/airfilter?
  15. 1cc

    1cc Guest

    Sounds to me like the new spark plug lead could have a break in it. What sort of lead did you replace the original with. If it is a silicone one these break very easily. Replace with a wire lead & try that.
  16. No. I checked the intake before I put the new carb on. In fact, the only way I could get the carb on there was to pull the intake, mount the carb on intake, and then mount the assembly back on the head. Clearance is very tight.

    At first, I used a new automotive silicon wire. I had issues immediately and put a new copper-stranded wire on there, just like the original. The boot is a new NGK, as well. It started easier, but it still didn't do anything right but start and idle.

    I got in touch with an old friend of mine who has a lot of magneto experience. He asked me if I replaced the magneto rotor and I did not. Well, after putting the jug back on and replacing the rotor, the engine won't fire anymore. I know the rotor is on the right way, and I'm sick of messing with it right now. POS.
  17. magneto rotor

    Hello, there are only 2 things to know about magneto rotor:
    A) installed correctly in proper direction, key in keyway?
    B) Has magnet lost it's permability???
    test magnet with 1/4 flat blade screwdriver, if the blade on the flat is really "stuck" on the magnet, ok, if you can almost "bounce" the blade on and off the magnet......replace it, REMEMBER the north pole is usually noticibly stronger than the south, this is normal, Mike
  18. ibeenjammin

    ibeenjammin Guest

    I am having similar problems as the original post, although I never lost my spark plug, nor herd a loud pop. Throttle response is just very slow/sluggish all of a sudden, it seems like it takes forever for the engine to warm up. I have replaced the intake gasket twice now. the bike just doesn't have the pick-me-up it once had. Please update us on your bike, has anything improved yet? My bike feels as though I am not getting the compression that I once had. I am going to try the beer can trick on the intake manifold and the washer as well. I hope it fixes my situation.

  19. Poodlebombs

    Poodlebombs Guest

    Wow, I have the same problem. I already rigged up the beer can and popped an o-ring in the sucker, still having problems. Throttle/rev is incosistant with my accelerating. I dunno what's going on, and i'm still in break-in.

    The carb is too tight of a fit on mine as well, so I flipped the intake upside-down and mounted the carb on straight. I didn't suppose it would effect anything, but the angles are a little different with the intake upside-down. I don't think this has an effect on my problem, but could this have any other side-effect? or negative effect on the engine?
  20. gone_fishin

    gone_fishin Guest