Engine Trouble Altitude sensitivity???

Discussion in '2-Stroke Engines' started by Sean Healey, Aug 20, 2012.

  1. Sean Healey

    Sean Healey New Member

    Another Newbie here - I just put together my first 2 stroke 48cc bike. It's acting really strange. I live in the White Mountains in AZ, and THINK I have the idle adjustment screw right, but it NEVER seems to idle!!! I have to control the speed and throttle by pushing in the kill switch. THAT ISN'T right.

    I took a ride down the hill (neighboring town maybe 3 miles away) to show the ride to my buddy, and we noticed all kinds of condensation on the air filter (too much gas). So I backed out the idle adjustment screw another turn. On the way home, the bike makes it okay on flat ground, but then dies half way up a half mile hill.

    I am wondering is it something I did incorrectly, or am I screwed going thru different altitudes? These 2 strokes are pretty basic, so am I gonna have to just search to find a decent 'happy-medium'?

  2. motorpsycho

    motorpsycho Active Member

    it sould be that your float level is too high which will cause the carb to flood over.
    yes, altitude makes a difference when it comes to jetting the carb, but once you get it jetted right, minor changes in altitude shouldn't really affect how it runs.
    make sure that you don't have an air leak at the intake - cylinder gasket or where the carb goes onto the intake manifold.
    a high, uncontrollable idle can mean you have an air leak.
    when it doesn;t want to idle, it can be a sign that it's flooding over.
    fuel on the air filter is common on a 2 stroke without reed valves (such as these china engines) because a little fuel is always being spit back out of the carb.
    But if your filter is soaked, that would tell me that the carb might be flooding over.

    dumb question, but are you sure that your choke isn't stuck closed?
    If the choke is stuck closed, this would give you the results that you are describing.
    another thing to check is to make sure that the main jet didn;t unscrew itself and is laying in the bottom of the float bowl.
    this is common with the nt carbs too.

    your idle screw has nothing to do with the air-fuel ratio.
    so by you turning your idle screw out another turn, did nothing but lower the slide in the carb, which will lower the idle speed.
    if your engine dies going up hill, that's another sign that the float level may be wrong.
    The carb could be running out of gas before the float bowl can refill.
    especially when going up hill because the carb is at an angle at that point, which puts your fuel in the float bowl at an angle.
    the float should be set to where the float bowl is full, but fuel is not coming out of the overflow tube or making the carb flood over.

    I may be wrong about the float level, but it;s worth checking.
    your engine shoudl start, and idle at a steady rpm. it should never change unless you twist the throttle.
    your engine should sit and idle all day long without touching anything.
    if you have to adjust your speed by using the kill switch, something is definitly wrong.

    are you absolutly positive that you have the carb slide installed correctly?
    it can go into the carb 2 different ways, but only one way is correct.
    the slide has 2 slots in it (a long one and a short one).
    pull the slide out of the carb and make sure that you have the long slot to the right of the carb (when looking at it from above). the long slot in the slide needs to line up with a pin that's cast into the inside of the cab body.
    the short slot should line up with your idle screw on the left side of the carb.
    if you have the slide in backwards (long slot to the left, short slot to the right) you will not be able to adjust your idle, and the slide will hang up and stick...causing an uncontrollable, high idle and no throttle response.
  3. pedalman

    pedalman Member

    Look at some of Jaguar's posts, I think he had altitude issues...
  4. jaguar

    jaguar Well-Known Member

    Yeah I was living at 8500 ft. Required leaner jetting and more compression. But anyway I say throw that chinese piece of junk away and get a good carb. Click on my link to read more.
  5. Sean Healey

    Sean Healey New Member

    Thanks guys! I am pretty sure the slide is installed correctly. I got rid of the twist throttle and threw a modified thumb throttle on the bike. The thumb throttle accelerates the bike when I'm going up a hill. I went ahead and dropped the bowl and backed out the float a few twists, hoping that would correct the flooding. I took it for a spin - the results were minimal. The idle has dropped down a bit, but when I put in the clutch - the motor still guns. I also tightened the carb to the intake manifold (looks like an overgrown thimble!!!) Oh yeah, the choke seems to be wide open, also. (The engine makes less noise when it's closed). Maybe I'll take Jaguar's advice and scrap that Chinese carb!!! This is the first time I've messed with building a two stroke motor-bike, so I'll learn as I go!!!