Whats wrong with my 49cc 2 stroke engine? PLEASE HELP!

Discussion in '2-Stroke Engines' started by rob0101, Aug 10, 2010.

  1. rob0101

    rob0101 New Member

    I have an engine that looks exactly the same as this.


    The problem is that it idles fine with the choke on/closed, but when I open the choke it revs like crazy. And if I rev the engine with the accelerator it dies.

    So far ive taken the engine to bits and given it a really good clean with wd-40, carb cleaner and compressed air but this has had no effect.

    If someone could tell me whats wrong or what I need to adjust/fix/replace that would be great!

    P.S. im having real trouble finding any information about this engine online so if anyone has some I would be very interested.

    Last edited by a moderator: Dec 16, 2015

  2. GearNut

    GearNut Active Member

    I would start by making sure that the throttle in the carburetor is closing all the way down to idle speed. It sounds like it is stuck partially open, or the idle speed screw is turned in too far.
    Also check the throttle cable for any kinks or bends which would prevent the cable inside it from moving freely, preventing the throttle cam from moving to closed position.
  3. rob0101

    rob0101 New Member

    Is the throttle in the carburettor the cylinder with a hole in it that turns when you pull the accelerator? If so when im not revving it closes so I cant see through the carb. So not sure its to do with that, will check again now though just to make sure

  4. adb140275

    adb140275 Member

    its WAY too lean, you need to take the carb apart and clean it.
  5. robimagu

    robimagu New Member

    Ensure that you've correctly installed the needle in the slide. The needle with the "c" clip should be UNDER the silver disk with the slit in it. I've seen pictures posted on this forum with it installed incorrectly. If it is install wrong, the needle will be pulled up with throttle application, but it won't reset properly causing high revs.
  6. rob0101

    rob0101 New Member


    adb140275 - the carb is spotless, lol just to be sure i have cleaned and double cleaned it so im pretty sure its not that.

    robimagu - "c" clip? silver disk with the slit in it? im lost! below is a diagram of my exact carb and a photo of my actual carb. if you could explain more?


    as a thought, how easy do the fuel filters on the end of the hose in the fuel tank get blocked? adb140275 says its running lean, could it be clogged?

  7. Bonefish

    Bonefish Member

    Your throttle arm stop screw is too far in. It is causing your carb to be open, I can see from the picts and it is not fully closing. You need to back off the throttle arm stop screw. Pictured in your actual carb pict in the top right hand corner. back it off so that the circle/opening is not showing when your throttle arm is relaxed.

    Hope this helps.
  8. Bonefish

    Bonefish Member

    opps top left hand corner
  9. rob0101

    rob0101 New Member

    thanks Bonefish, i thought as i could not see straight through that it would be alright but i will adjust that screw in the morning and hopefully the results will be good!
  10. motorpsycho

    motorpsycho Active Member

    yep, in the pic it looks like the throttle blade is wide open because the scew is in too far.
    when you close the choke, you are starving the engine of air, and that's why it will idle down.
    open the choke and a rush of air is getting sucked in causing the rpm's to skyrocket.
  11. Bonefish

    Bonefish Member

    While you got it apart.......

    Doing this will isolate some variables and make any further trouble shooting easier if any other problems occur.

    Backing off the throttle arm stop screw so that just the little nub on the screw or just a couple of threads show on the back side of the stop screw black support brace should be a good mark to measure.

    Next, run your throttle cable like it would be installed on your bike,(with all the bends in the cable) but do not have it hooked up to the engine/carb. Twist the throttle grip and make sure the cable runs smooth in the cable housing and does not get hung up with any bends in the way you have it run to the engine. You might wanna add some 3&1 oil inside the cable housing, so that the cable is lubricated, but make sure you clean off any access at the ends so it does not attract any dirt/grime.

    Then, rig it up like you are going to run it, start engine, and adjust idle screw.(the one that has the spring on it) so that your engine sounds like cat sitting on your lap with its motor running(purring) while your petting it. Not too much( or the cat sinks his claws into your leg) not too little(or the cat keeps looking at you to pet it some more).

    I have the same/similar engine. It has lots of power, gearing this inexpensive engine properly will make it outshine expensive engines that have fixed gearing.

    This should give you a decent foundation to build upon.
  12. rob0101

    rob0101 New Member

    Cheers Bone fish, i have adjusted the throttle arm stop screw so that the little nub on the screw shows and set up the throttle cable etc so its all set

    just to make sure, is this the idle screw with the spring you are talking about?


    ive never touched this screw before but the engine is second hand so the previous owner may well have. how would i go about adjusting it? turning it which way, how much, does what? and how can i tell if im doing damage lol

  13. GearNut

    GearNut Active Member

    The screw with a black arrow pointing to is is a fuel mixture screw. It regulates the high speed fuel circuit.
    If you turn it in too far you will damage the fine tip of the screw and the precision fuel port that the screw works in conjunction with.
    Turn the screw out to enrichen the high speed fuel circuit, turn it in to lean the high speed fuel circuit.

    The screw with a red arrow pointing to it is the idle speed adjusting screw.

    Attached Files:

    Last edited: Aug 13, 2010
  14. motorpsycho

    motorpsycho Active Member

    thanks for correcting me....i know NOTHING about this carb and i assumed it was a typical style carb.
    I will delete my post so he does not get the wrong information.
  15. GearNut

    GearNut Active Member

    It's cool, motorpsycho.
    I had that exact carburetor on my go-ped before I went to a high performance one.
    It is alot different than a HT carburetor.

    Thank you very much for your concern, alot of folks would have just left their post in place.
    You are a good person!
  16. rob0101

    rob0101 New Member

    Right, im guessing if my engine is dieing when i accelerate that its not getting enough fuel, so i will unscrew the screw with a spring on it a little bit to allow more fuel in, and see how it goes!

    P.S what is a good/correct ratio of fuel to oil to put in this engine, im guessing 25:1 but is this abit oily?

    hoping to try the engine with these few tweaks i have made tomorrow evening :)

  17. GearNut

    GearNut Active Member

    32:1 has never failed me.
  18. rob0101

    rob0101 New Member


    So i got home today, made up some 30:1 fuel, put it in, AND...nothings changed :(

    this is exactly how the engine is behaving - with the choke nearly on fully it idles good, but if i rev it, it dies, and if take the choke off it dies.

    Im completely out of ideas? thanks for all your help so far

    ...but what next?

    could it be the engine is getting a lack of fuel?

    Last edited: Aug 15, 2010
  19. GearNut

    GearNut Active Member

    The choke plate restricts air flow resulting in a richer air/ fuel mixture.
    So yes, the engine is suffering from a lack of fuel or a bad air leak between the carburetor and cylinder.
    If the engine was sitting around for a while before you got it, with fuel in the carburetor, your problem could be caused by gum and varnish buildup inside the carburetor.
    I would clean the inside of carburetor next. They can be tricky as there are little springs, a fuel valve and somewhat fragile reed valves inside them.

    Edit: ONLY if it has been sitting for a long time.
    Last edited: Aug 15, 2010
  20. GearNut

    GearNut Active Member

    I checked on a web site that sells the RacerX scooter, which is what I have, and they recommend 32:1 oil ratio.
    Ironically that is what I run in all my 2-strokes anyways.