engine shakey at mid speed

Discussion in '2-Stroke Engines' started by AdamT, Jun 4, 2009.

  1. AdamT

    AdamT Member

    Whats going on. I have a Dax 67 almost through 3/4 or a gallon so still running 16 to 1. grood smooth power at lower speed but then at mid speed it is rough. once it gets past that, the top speed is smooth again sometimes i can help it through the rough stage by peddling. What is going on I have my mix needle on the second from the top, or 3rd from the point. I tried going richer and leaner with the needle but second from the top works best for me. Is this normal? havent encountered any other MBs so not sure what its supposed to be like.
     

  2. pdxrhett

    pdxrhett Member

    Well, are we talking about vibrations, or shakey power? Or is the motor jerking the bike around?
     
  3. AdamT

    AdamT Member

    sorry its more like the enginde gets weaker at mid speed, then as i peddle it or just hang on through the chugs it smooths out with at higher speeds and gets more power.
     
  4. pdxrhett

    pdxrhett Member

    Do you have any upgrades installed?
    Some upgrades only work in a certain rpm powerband (i.e. tuned pipes). Also, with a 4 stroke motor, the powerband is pretty equal (compared to 2 stroke) all the way through the rpms, but with a 2 stroke engine the powerband is at a much higher rpm than a 4 stroke
     
  5. AdamT

    AdamT Member

    no upgrades just an un even power band. im using premium gas and still breaking in at 16:1 almonst have a gallon through it.
     
  6. RMWdave

    RMWdave Member

    go for a ride and try to work it out while you listen to the exhaust note. when it becomes sputtery or off tune slack off all the way down to idle and slowly bring it up in tune again.
    try to do this untill you have your flat spot worked out. Sounds like a break in issue to me it may not go awa if you have ridden too hard through the top end by now, but you can try
     
  7. 2stroketech

    2stroketech New Member

    Different diameter carburetors will give you different power curves. Now I know that you have a stock set up, so I would look at your intake manifold and your transfers. It is possible that they have some casting flaws in them that are giving you some hick ups.

    Also While you have the intake manifold off you might want to check to see if the gaskets are matched to the ports. This will also cause you problems.
     
  8. AdamT

    AdamT Member

    dang yeah i have definately ridden the top end pretty hard it is almost through its first gallon now i will try to do that dave. I will also check the gaskets but i am prety sure they are in good condition. Thanks guys
     
  9. fetor56

    fetor56 Guest

    Break the engine in first & IF u still have the same problem get back to this thread.No point in trying to diagnose something from an unbroken/inconsistant engine(u don't know what's normal)
     
  10. RMWdave

    RMWdave Member

    for sure mate, try and work out your flat spot 9 times out of ten you can in the early stages to get it all back.
    the point is to not force it to top RPM (through a sputter) you want to go from base to sputter back off and again. after about ten minutes of doing the climbs and falls you should notice a slight pickup.

    have it a try, you understood what im saying so let me know how it works out!
    -dave
     
  11. RMWdave

    RMWdave Member

    you have to listen to the exhaust note and be consisten on the throttle to keep it making the music :)
     
  12. AdamT

    AdamT Member

    ok i will try to back it off and rev it back. so far it just comes back rough when i throttle back up. i will try some more i hope i havent toasted my engine
     
  13. RMWdave

    RMWdave Member

    my idea here is that you shouldnt hit the rough spot.
    when its "getting there" and you know it, return to idle. come onto the throttle very slowly and consistently hold tune
     
  14. Junster

    Junster Member

    Your probably doing what's called 4 cycling at mid rpm's. The motor is only firing on every other stroke. It's kinda normal when braking in. Your next gallon of gas goto 7 or 6 oz of oil. That will help, also your at the point that some extended periods of higher speed will finish setting the rings. As it gets broken in the rest of the way and you reduce the oil it will get alot better. You really can't tune the carb very well till it's broken in all the way. Check around the head for any oil. Your getting about to the point you may need to re-torque the headbolts.
     
  15. RMWdave

    RMWdave Member

    word to junster, hes explained the problem id helping you work out!
     
  16. AdamT

    AdamT Member

    hey thanks guys I am getting close to the end of Gallon #1 at 16:1. It is gettin better and I will check those bolts.
     
  17. Skyliner70cc

    Skyliner70cc Active Member

    Flat spot caused by extreme richness at low end followed by leaner mixture when the needle valve takes over.

    The easiest fix I've found is to add a slant high compression head. It automatically leans out the low end and the high end is richened by needle clip adjustment.
     
  18. AdamT

    AdamT Member

    yeah that would be nice those things look sweet.
     
  19. AdamT

    AdamT Member

    OK switched to 32:1 with standard 2 stroke oil. haven't gone on any super far ride but have definitely warmed it up once. The engine still hits a spot at mid speed ( maybe where the main jets take over? ) and it chugs, once through the chugging stage it accelerates nicely. It does it more when going up hills. do i need more oil than 32:1 I checked the plug ant it looks black/ brown and slightly wet, not gooey and clogged...
     
  20. AdamT

    AdamT Member

    switched the needle pin settings and and no improvement anywhere. also switched to 87 octane from 91 and no real changes.
     
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