Engine Trouble cant get full power?

Discussion in '2-Stroke Engines' started by pedropete91, Sep 3, 2012.

  1. pedropete91

    pedropete91 New Member

    hey there i have an 80cc motored bike and when im trying to get top speed it wont let me ping it?. It bogs down on full throttle? so u got to hold it just before flat to sort of build up speed?.

    -A80 (chrome)
    -speed carby
    -36t sprocket
    -premium unleaded 98
    -s.b.p expansion chamber
    -26" southern star

  2. Fabian

    Fabian Well-Known Member

    The words "Chinese bicycle engine" and "full power" are a paradoxical oxymoron. They should not exist in the same sentence.
  3. Fabian

    Fabian Well-Known Member

    Be happy with the power that you have, because more power is inversely proportional to how much time is spent trying to tinker with the system.
  4. Ludwig II

    Ludwig II Member

    How to make a small fortune out of tuning 2 stroke engines:

    Start with a large fortune.
    cdcsfinest likes this.
  5. Lunardog

    Lunardog Member

    Too funny.....too true, but too funny.
  6. FelipeCobu

    FelipeCobu Member

    If I do understood it well: At 3/4 throttle it runs nice, full throttle it starts to fail. Looks like you have a small jet in your carb. What carb? What fuel/oil ratio? What needle position are you running?

  7. adrian101

    adrian101 Member

    If you answers these question i can give you the right solution to your problem :D also how far is your idle screw in on your speed carb.
  8. motorpsycho

    motorpsycho Active Member

    the main jet is too lean (too small)....causing it to bog at w.o.t.
    also, get rid of the 98 octane fuel and run the cheap 87 octane struff.
    high octane fuel is a waste of money in one of these engines, because they are low compression.
    it will run better on lower octane.
    what fuel - oil ratio are you running, and what oil are you using?

    the needle position in the carb has nothing to do with full throttle.
    the jet needle is only in effect from idle until about 3/4 throttle.
    after 3/4 throttle, the needle is completely out of the main jet well, and the only thing doing the fuel metering at full throttle is the main jet.
    changing the position of the needle to fix a full throttle bog is useless.
    Last edited: Sep 4, 2012
  9. fm2200

    fm2200 Member

    I recently had the same thing, the way to check if your getting less fuel to the carb due to the fuel inlet that the fuel line slips over. First thing to do is remove the screw on the side of the bowl on your carb. After removing the screw you should get fuel spilling out. Once the bowl is empty then the fuel should be coming out if everything is good. If there is a very small trickle only or only drops then your brass fuel inlet is the problem. Remove the brass fuel inlet and clean it with a small diameter wire. This should make your problem disappear.
    Passenger66 likes this.
  10. pedropete91

    pedropete91 New Member

    cheers for the advice people. All i wanna do is be able to beat my mate who has a f80 stock nt carby and a 40t i dunno why mines slower it shouldnt be. Yes 3/4 is fine but full throttle it bogs down (speed carby stock jet)(200ml/5L fuel)(needle position is 2nd to top) only just changed it thought it was running abit better.(shell premium unleaded 98 high octane)(idle screw is about 2 or 3 turns in)(valvoline oil)
  11. pedropete91

    pedropete91 New Member

  12. jaguar

    jaguar Well-Known Member

    drill out the main jet about .05mm more or change it to a fatter jet.
  13. Fabian

    Fabian Well-Known Member

    Ahh, i see you are in Adelaide.

    That kind of behaviour will see motorized bicycles become viciously targeted by the police as in NSW and Victoria.
    I can't help thinking that ripping up and down the street or bicycle paths with your mate (trying to go faster and faster) will attract attention; all the wrong kind of attention and f*ck it up for everyone else who is desperately trying to quietly and stealthily fly under the radar; attracting as little attention as possible, because they need their bike for transport.
  14. V 35

    V 35 Member

    The chinese engines need to burn up a few tanks of fuel before they break in. The clutch, in particular, tends to be tight and whiny,
    robbing torque. After break in, torque improves. Torque head,
    tighten nuts, keep first runs short, allow long cool offs, and the motor can be reliable, and satisfying.
  15. motorpsycho

    motorpsycho Active Member

    you say "valvoline oil".
    are you using motor oil (such as 10w-30) ? or are you using 2 stroke oil?
    what is your gas - oil mix ratio (like 40:1, 32:1, 20:1) ? how many ounces of oil per gallon (i don't understand liters and all that metric stuff...lol).
    you have a 36 tooth sprocket?
    what size wheels does your bike have?
    how tall are the tires?
    if your friend has taller wheels and taller tires, his bike will be faster on the top end. wheel & tire size affects the gear ratio.
    if he's running a 40 tooth sprocket but has 26" or 29" wheels, and you're running a 36 tooth on 20" or 24" wheels, his will still be faster because his final gear ratio will be higher than yours.
    it sounds like your carb needs to be re-jetted to give you a richer air-fuel ratio(or the jet that's in it needs to be drilled out as jaguar suggested) it sounds like it's running too lean (too much air, not enough fuel) with the w.o.t. bog / loss of power.
  16. pedropete91

    pedropete91 New Member

    what kind of behaviour? Mate i never said i rip up and down my street with my mate (trying to go faster and faster) LOL. Cheers Jaguar will do! valvoline oil yes 2 stroke mix 20:1 both same size wheels 26" dont no about tyres but shouldnt matter that much as i got the 36t. Cheers
  17. Fabian

    Fabian Well-Known Member

    You beat your mate, then your mate decides to beat you and on it goes - by definition that's called trying to go faster and faster; quite possibly on a bicycle that was never designed to go at the speeds you want to achieve.
  18. crassius

    crassius Well-Known Member

    usually, if you're lean, applying just a tiny bit of choke will add power - if not, you're probably not lean
  19. fm2200

    fm2200 Member

    Did you fix your problem with the 3/4 throttle, if not try reading my post you will be back to normal. cheers
  20. TomONaBike

    TomONaBike New Member

    If you have already rode your bike for a few gallons of fuel mix, you may be able to lower your oil mix ratio. Move down to 32:1 gas oil mix, or a little less. It will make it seem like the engine burns hotter and harder.