Rough running

Discussion in '2-Stroke Engines' started by connerdsny, Oct 20, 2015.

  1. connerdsny

    connerdsny New Member

    I just put together another 2 stroke bike after the first one cracked the bike frame. I used the same engine, but replaced several of the bolts and gaskets, and smoothed the head and cylinder in the hopes that my engine would run better. I noticed a bogging problem before my bike frame cracked, and it's only gotten worse since I put my new bike together. Since I'm running out of things to diagnose, I figured I'd post something here and let someone more knowledgeable guide me. On my previous bike, the engine would run great for 10 seconds at top speed, then suddenly bog down and decelerate. Now, the engine is a constant bog but will suddenly pick up after riding for 5 minutes. Ive replaced way too many parts on this engine, and I don't know where to look. Any help is appreciated!
    New carb, new spark plug, new gaskets, fixed wiring, new fuel feed.
     

  2. mikedabomb

    mikedabomb Member

    Check out on google tuning the fuel and air ratio of a two stroke. Sputtering, not accelerating, blue smoke/oil out of exhaust - rich air/fuel. High idle, holds rpms after quick rev, wants to take off, no visible smoke/oil from exhaust - lean air/fuel.
     
  3. connerdsny

    connerdsny New Member

    Thanks, Mike! Although I've spent way too many hours trying to tune the carb with little resolve- I'm beginning to doubt thats the problem. It's had a very consistant decline in performance since I started riding... the intermittent bogging is what's confusing me- it seems to have no pattern other than occurring more often the longer I ride. could a leak in the engine case cause this?
     
  4. crassius

    crassius Well-Known Member

    I'd suspect that your motor mounts are allowing some shake in the motor at certain revs which is then shaking the carb and foaming your fuel in the bowl - slows down like ign missing, then picks up for a bit, then slows down again and so forth.
     
  5. Timbone

    Timbone Active Member

    If there is a weakness in the bike frame, these little two strokes will bring it out. I think the best approach is to consider a frame (unenhanced) to have a working life of one year. Always keep an eye out for a new frame.

    Bogging out on the top end (with predictable 4 stroking) is a classic symptom of too rich mixture. The solution is simple: change to a smaller jet in the carb. That leads to another problem: these 2 strokes start best with rich mixture. It may be that the perfect jet size for top end riding can make the engine hard to start.
     
  6. connerdsny

    connerdsny New Member

    Thanks for the help! I need to make new mounts anyway, so I'll get on that and see if that helps. I'll also order some more jets, as this new carb I got didn't come with any.
     
  7. jaguar

    jaguar Well-Known Member

    I'd suspect a leak at the crank seals.
    the right side of the crankshaft has a lip that the seal can catch on, so even a new engine can have that seal leaking due to not seating correctly.
    does it take a while for the idle to settle down to its normal putt-putt after twisting the throttle and then letting it go? that would indicate a leak at the seals or at the intake manifold (usually where the carb connects to it)
     
  8. connerdsny

    connerdsny New Member

    Yes, it does take a while to return to idle. I've replaced the intake gasket, and the carb/intake seal was leaking at one point but I think it is fixed. How would I check the crank seals?
     
  9. jaguar

    jaguar Well-Known Member

    take the magneto and stator coil off
    take the spark plug off
    spray the seal area with soapy water (using dishwashing soap)
    turn the engine over and watch for bubbles
    then on the right side take the primary gear off and do the same
    bubbles indicate a seal leak
     
  10. connerdsny

    connerdsny New Member

    Okay, thanks! I'll try that tomorrow when I get a chance.
    For now, here are some pictures since I never posted any.
    20151028_125950.jpg 20151028_130002.jpg 20150829_103711.jpg
     
  11. butre

    butre Well-Known Member

    get rid of that rubber. it's the source of every problem you've ever had
     
  12. jaguar

    jaguar Well-Known Member

    Why did you cut a hole in your clutch cover and why isn't there a screw holding the primary gear on?
     
  13. connerdsny

    connerdsny New Member

    will do- thanks. I put it in after the last frame cracked, does it actually cause that many problems?
     
  14. connerdsny

    connerdsny New Member

    the primary gear screw came out at one point while riding and blew that hole in the cover. I actually did not realize the screw had come out again until you pointed that out... that sucks... I had even marked it to make sure it wasn't coming loose. Is there a good place to get another one?
     
  15. crassius

    crassius Well-Known Member

    that first frame cracked because your motor was badly mounted - those screws for the water bottle and the bossed areas they screw into will not allow a motor to sit flush with the frame - one thing to be done is to take out the screws and grind the area flat, but I prefer to cut a piece of PVC and drill a hole in it to allow the bossed area to sit in the hole while motor mound then sits flush with the PVC

    no rubber should ever be used in a motor mount - add a piece of PVC between rear block & frame too

    that crank screw should be put on with the lock washer and driven in firmly with an impact driver, I know of no easier way to get a slotted screw in firmly enough
     
  16. SunkyWorks

    SunkyWorks Member

    The the metal around the crack in the frame tube is gray/silvery. This is a sign of a Chrome-Moly frame. The more
    expensive Chrome-Moly frames are Butted and are thinner in the middle and are thicker at the tube end welds. If this
    is the case then this frame is not the best to mount a in-frame motor. I would avoid bikes with a sticker on the
    seat tube that has the word "Butted".
     
    Last edited: Oct 29, 2015
  17. connerdsny

    connerdsny New Member

    today I checked the crank seals and ordered new parts. There is definitely a leak on the magneto side, how should I approach this?
    I ordered a new primary gear screw, gear cover, and stronger head studs (it looks like there is plenty of oil leaking around the head, and I'm still using the original studs... figured it wouldn't hurt)
     
  18. jaguar

    jaguar Well-Known Member

    try to pry it out using a jewelers screwdriver and if it won't come out then
    use a torch to heat up around the seal before prying the seal out
     
  19. connerdsny

    connerdsny New Member

    Got it out, is there a good place to get a new one? Or should I reuse this one?
    Thanks for all the help.
     
  20. jaguar

    jaguar Well-Known Member

    really? You are asking if its ok to reuse a bad seal?
     
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