Engine Trouble Acceleration without Throttle

Discussion in '2-Stroke Engines' started by CarbonBikes, Sep 8, 2013.

  1. CarbonBikes

    CarbonBikes New Member

    So I decided to try to start selling these bikes. I've only made a few but this engine (a 66cc skyhawk 2-stroke engine) is giving me some issues- the bike accelerates without me giving the engine any throttle. So as soon as I start peddling, let the clutch out, the engine starts fine, but then it just starts accelerating when I'm not giving it any throttle whatsoever.

    Things I've Tried: I tried switching heads from another engine that works perfect but that didn't seem to solve anything (the reason I did that was because the person who sold me the engine said there might be a hole in the engine somewhere and is causing a compression issue or something....?)
    Well anyway, that didn't do anything so I replaced the gasket, which didn't do anything. My final attempt at fixing the issue was to switch carburetors from a working bike to the one I'm having issues with. Which (you guessed it) didn't do anything.

    Things I've double-checked: I made sure the throttle and float wasn't stuck in the carburetor. I made sure the throttle cord wasn't stuck on the inside of the throttle.

    I can't think of anything else. Anyone have any ideas? None of my other bikes accelerate the way this bike does. And when I pull the clutch the engine revs instead of idling.

  2. zippinaround

    zippinaround Active Member

    sounds like it could be an air leak somewhere!
  3. CarbonBikes

    CarbonBikes New Member

    As I said, my engine dealer told me that what he didn't say was how to find it and how to fix it... Where would I find an air leak and what does this mean?
  4. zippinaround

    zippinaround Active Member

    just type air leak into the search bar at the top. have you tried adjusting the idle screw? when i bought my bike the idle screw was tightened in full so as soon as it started it was at full revs!
  5. bluegoatwoods

    bluegoatwoods Well-Known Member

    One place to look for an air leak is right where the intake manifold bolts to the cylinder. There should be an O-ring there. Make sure it's not twisted or missing, stuff like that.

    But your symptoms don't sound like air leak to me. It sounds as though the throttle slider or barrel, whatever it's called, is stuck. You mentioned that you changed out the carburetor, I know. But I'd still have a look at that.
  6. zippinaround

    zippinaround Active Member

    ya thats what i was thinking too but he said he has already double checked that the throttle wasn't stuck. but just in case make sure when your putting the slider in that the little notch in the end is lined up with the idle screw and the slit is at the other side.
  7. bluegoatwoods

    bluegoatwoods Well-Known Member

    For that matter, I ought to clean up my sloppy thinking and advice.

    There's no O-ring at the meeting of intake manifold and cylinder. That's a gasket. Could be trouble there.

    And the o-ring is located at the meeting of the carburetor and manifold. And there could be a leak there, too.
  8. KihOshk

    KihOshk New Member

    Not to be a downer, but an aged voice of wisdom: you might want to hold off on your business venture until you are more familiar with the basics of these temperamental little engines. Also, since you're "of age", you can be exposing yourself to some very serious legal-consequences if someone hurts themselves or someone else on one of your builds. I have become somewhat of an "Uncle 2-Stroke" (that didn't sound right!) in my town. I taught/helped 5 guys with their builds as I was the first in my region to have an MB. I had been approached to actually build-for-sale, but I refused for two reasons: the legal risk, AND I don't need irresponsible/disrespectful riders sulliing our hobby.
  9. HeadSmess

    HeadSmess Well-Known Member

    agreed. 100%.

    not only are there legal implications, theres proficiency.

    unfortunately, you will have customers asking exactly what you are asking right now.

    you will have to know whats wrong, and how to fix it. so, sorry. no advice from me. i know whats wrong too ;)

    if you get a phonecall "my bikes not going", will you be able to sort it out for them and have it running in 5 mins over the phone?

    legally, do you have ANY qualifications, either as a small engine mechanic, or as an engineer?

    you have only made a few. wait until you have fifty or so done. even then, there will be bugs with almost every build, unless every one is the same frame, same engine, same same same. bit generic?

    can you relace a wheel with HD spokes? machine a bush or hub to fit a sprocket? lay a good, solid bead with a tig, oxy torch, or braze?

    i know the idea of putting an engine on a pushy is great, but unfortunately these things need to be assembled correctly, especially if your reputation depends on how well they hold up and how well you can repair them when necessary.

    if someone is crippled, injured or even dies.... its your fault. thats what the courts will say. what will you say?

    sorry :( im not dissing you or saying its impossible!

    theres just a few things that need considering first.

    other than builds for a select privileged few, i dont build bikes for other people. too many headaches!
  10. SuedePflow

    SuedePflow Member

    Have you verified the barrel inside the carb is not hung open? Assemble the carb with the cable attach and peak into the outlet. If it is hung open like this, then it will cause the problem that you're describing.

    When it happened to me, I determined that the cable adjuster on the top of the carb did not allow enough adjustment (either that or the cable was made too short) and it was hanging the barrel open. I ran a drill down the adjuster so that the cable sheath would sit lower and the barrel could close make contact with the idle screw.
  11. CarbonBikes

    CarbonBikes New Member

    The engine was lined with some kind of kerosene or something. I think the engine was already used even though I pay full price for a new one. The guy I got the engine from said that he had a guy mount a nos kit to his bike and ruin his engine. I think he sold me the head of that engine to me with the rest of the kit. I guess the engine still had some of the nos stuff on the inside because it's running fine now. I guess it had to "burn off" or something? not sure. The gasket was fine, the head bolts were all tightened like they should be. Nothing wrong with the carburetor because I took my throttle cable, throttle, and carburetor off my bike and switched it out- still had the problem. So i put all the original parts on the bike and eventually the engine settled down. Soo yeah. Thanks for all your help with it though. Thanks for all the responses.
  12. CarbonBikes

    CarbonBikes New Member

    I say the same thing anyone else would say. That's like trying to sue Honda for crashing one of their cars off of the lot. It's not the dealers fault for the stupid things the drivers do with cars. Same with trying to sue Harley just because some donkus decides to go off a ramp.

    I've had engineering experience working in foundries for a few years. I know a bit about engines these ones are simple enough. I know how to weld, solder, etc. Thanks for the tips and heads up. I figured if people signed a form with a witness that it would hold up in court (plus my previous argument). I wanted to ask a legal advisor if a signed form basically saying that I'm not responsible for whatever the customer does on the bike and to have a witness sign as well (if doing all that would hold up in court or not).

    I have thought a lot about it. Thanks for your concerns, definitely gave me a few more things to think about.