Engine Trouble Question on a little power loss when hot?

Discussion in '2-Stroke Engines' started by geebt48cc, Sep 23, 2012.

  1. geebt48cc

    geebt48cc Member


    The bike is running very well, but once the engine gets a few miles on it, it loses power?? See, it has much stronger torque or pulling power the first few miles, then fades???????????????? It still runs well, but loses its pulling power up same hills it just pulled earlier?

    Just asking? I'm using NGK B5 and B6-----with new Jag CDI.

    Glen (Chopped plugs, and all are burning chocolate)

  2. Purple Haze

    Purple Haze Active Member

    Sounds like you're running too rich. Try setting the needle one notch lower in the slide, and see if it runs better. I have the opposite problem, when cold it runs like ****, but pulls like crazy when warmed up. But hey, thats what the choke is for! Usually, these engines run well when the clip is in the second notch, but I had one 49cc that ran best with the clip in the highest notch. If this doesn't fix it, you'll need to jet the carb leaner, or get a different carb. The "speed" carb works well for me out of the box.
  3. geebt48cc

    geebt48cc Member

    Thanks Haze,

    See, the plug looks like it's been burning just right. I'm on third notch down on the carb needle. I could try the second, but beening I've milled head, I've read that with higher compression, it's smart to drop a notch to richer burn?!~ Anyway, like I said, the motor runs well, but looses a bit of torque after at running temp? I wonder if it would be smart to run higher octane? It's says thats better for higher compression heads............
  4. motorpsycho

    motorpsycho Active Member

    if the plug is chocolate, it's not too rich, it's perfect.
    the needle setting has no effect after 3/4 throttle so changing it probably won't help. climbing hills usually demands w.o.t., therefore, a needle height change won't do anything. the needle only affects the mixture from idle until about 3/4 throttle.

    no 2 carbs and engines are the same, so what worked for you may not work for someone else.
    besides that, the choke is ONLY for cold weather starting.
    if you have to flip the choke on after it's warmed up to get power...YOUR carb is too lean.
    you should never have to use the choke except for starting the engine when it's cold (and i'm talking like 50 degrees or less outside).
    a warm engine that makes lots of power when the choke is on is either jetted way too lean or you have an air leak that shows itself once the engine is warm and the intake gasket expands.
  5. motorpsycho

    motorpsycho Active Member

    yes, high compression demands higher octane fuel.
    but, if you have good power when the engine is cold, you should have the same power when it;s warm.
    unless you have a head gasket issue that shows up once the engine is warm.
    if you have a high compression head and it looses power when warm, the head gasket may develop a leak once the head and cylinder are warmed up. one or the other may not be perfectly true, and when alumimum heats up it expands, which may cause the head or the cylinder to slightly change shape, which may be causing a leak at the head gasket, lowering the compression and making it lose power.

    I don't know, just a thought.
  6. geebt48cc

    geebt48cc Member

    No, No, makes very good sense. I've very much checked (before and after) many times the head. I torque it at 12 foot pounds, every 50 miles or so. It's not only milled down, but I'm not using a head gasket. I use (Gasket Shellac) on head. It's been modified like that now for over 300 miles with out any leaks or issues. The whole area is very dry, with zero blow back.......Tight seal. Motor runs very well, just wants to loose torque after so many miles?..............but, it still runs out, and is burning plug right on the money................Total miles now at 665.....
  7. Purple Haze

    Purple Haze Active Member

    Not only would it be good to run hi- octane for compression, but most ethanol-free gas is only available in hi-octane. Your loss of torque, is it a serious loss? If not, I'd just accept it and move on. It sounds like thermo expansion, causing the bore to distort, or the rings. These engines are not metallurgical marvels (LOL) Also, the plating (coating?) on the cylinder wall is not known for its longevity, which could be causing a compression leak. Good luck, but it seems you have a pretty good running setup, don't expect too much from em.
  8. geebt48cc

    geebt48cc Member

    I do very much agree....I was just trying to figure out (even though it's running good) why it slacks down on pulling power after a few miles? I'm going to try the higher octane and see if that helps some?!.

    No, it's not a very serious loss of power, just the torque and MPH's fade away. Uno going up same hill later in ride? lol, I can't believe I have to then help it at times with the pedals?!~ lol.......But, when I first start riding, and it's cooler, it will pull very well.