Carby NT Carb Tuning Basics

Discussion in '2-Stroke Engines' started by AussieSteve, Dec 27, 2009.

  1. Tumbledove

    Tumbledove New Member

    Thanks for your very clear instructions Irish John. I still could not get the cable to budge at all tho. I may try again at a later time when I am not frustrated with the thing. It runs great without it right now, so I may just leave it alone before I "fix it" real good. :)

  2. rogernelson

    rogernelson New Member

    Hey thanks for the info. I checked my bike for all these parts. I changed some of my bike parts now.
  3. goodtime65

    goodtime65 Member

    If you are having trouble releasing the throttle cable than it may help out to remove it from the throtle handle and this will give you more cable to play with
  4. jeffuehrer

    jeffuehrer Member

    The Float Needle Jet Valve

    Thanks for all the pictures and descriptions of the carburetor.

    I have recently been having problems with my motor and discovered that the float needle jet valve had unthreaded and was swimming free nilly in the bowl causing havoc. I over tightened it though causing it to break off with a small chunk left in the threading. I had another spare carb and took the float needle jet valve out and proceeded to thread right behind the chunk lodged in there. the bowl is up tight against the main jet now but it is the one with a flathead notch so i'm hoping that fuel will still be able to flow up through the main jet. If it doesn't work what would you guys suggest I do? Thank you in advance.

    "If it ain't broke, fix it 'til it is."
  5. jeffuehrer

    jeffuehrer Member

    Well, It ran great for about 3 miles and I was like "yea, I fixed it!" no you didn't. The spare float needle jet valve dislodged due to the lack of sufficient threading due to the blockage from the previous float needle jet valve chunk. Using my will and ingenuity I devised a plan to unthread the chunk using a mere steak knife. I successfully dislodged the blockage and was thusly able to thread the entire length of the spare float needle jet valve...snug. Lesson 358 learned. Thanks guys, you are all geniuses!

    "If it ain't broke, fix it 'til it is."
  6. happycheapskate

    happycheapskate Active Member

    If the throttle cable is "stuck" or the carb slide will not move freely, it may be installed backwards. I did that once, and the bike started and took off full throttle till I killed it with switch. There is a groove on one side for a locator pin, to keep it from turning, and a notch on the other side where it contacts the idle screw.

    I got o-rings from Sick Bike Parts for the carb-to-manifold fitting and the little knurled cap where the cable goes in.
  7. jeffuehrer

    jeffuehrer Member

    Yeah, the slide notches were my first lesson a year ago. I haven't installed the slide backwards since then. I always have problems with the jet needle valve coming unthreaded. A guy I sold some unneeded parts to today suggested I use blue loc-tite but since snugging it up last night it's been running great. If it falls out again I'll know what to do. I don't have a kill switch. If I need to kill it I choke it or stop and hold the brake then release the clutch slowly. I know it is dangerous not having the kill switch but really the whole motor on a bicycle thing is dangerous if you think about it. Ladies first, safety second.

    "If it ain't broke, fix it 'til it is."
  8. Tumbledove

    Tumbledove New Member

    This may be my next move if and when I need to take the slide out again. I adjusted the c-clip position lower and she bogged. Then I went a notch higher, (the highest), and she bogged. So I just put the c-clip back where it was. I was looking for a little more top speed and to see what effect it may have in throttle response. All of this was done without any finesse whatsoever, :broken:pushing the needle and clip through the spring. The c-washer still abides quite content on my desk.

    As a side note, does anyone know why the idle screw does not seem to have any noticeable affect on the engine's rpm? I appreciate any and all replies. A safe 4th goes out to all!:patriot:
  9. lewsidius

    lewsidius Member

    hello everyone
    my engine starts but the bike doesnt take off
    i move the throttle open and no change in sound
    and i slowly come to a hault and the engine turns off
    the engine has a good sound and a consistent rythum
    i tried the bike before work after tightening the Throttle

    the bike idles then as i lose speed the engine gets quiter and i slowly come to a hault

    i took apart the carb and the slide is moving proper back and forth
    and the spark plug definatly has a strong spark (ouch)

    so i dont know what to adjust or whats wrong????
  10. lewsidius

    lewsidius Member

    i should also mention that its all me when the bike moves not the motor!
  11. lewsidius

    lewsidius Member

    hello again
    i adjusted the float
    and gas is leaking
    but i started the bike anyway
    and it actually moved
    its stupid i know
    but i was able to go pretty fast
    and i wanted to see if it worked and it did
    however it really over heated

    but its helped me establish that there is a shortage of gas going in

    it either barely gets enough gas and just idles
    or it gets too much gas and doesn't idle but it takes off and overheats

    and i only move the forks on the float ever so slightly to make this transition

    when i look at the gas line when there is not enough gas it fills just to the bottom of the filter on the line

    and when its overflowing
    that when the entire line is full

    im so close

    i currently have a separate thread on the matter (sorry) i just wanted to reach a bigger audience
  12. SdCruizer

    SdCruizer Member

    I just put on a bolt on larger filter k&n style
    I also bought 2 jets 72, 74
    Ive jetted a carb before on a scooter and knew when it was too large by the bogging at full throttle but I had more jets on hand and purposly started too large

    when I tried the 74 it ran fine, just seemed to loose top speed or didnt get to full speed quick enough hard to determine going up hills
    72 seems normal how I remember the stock setup felt like

    I will check the plug but I was wondering I read once about a tool you can use to check jet sizes, I think they were pins or something

    I want to compare the new jets to the stock jet hole

    Someone posted they ran a pipe and same filter and used the 74 jet, which makes me think my 72 at the least will be fine
    Since its a pain to change I never tried the stock jet
  13. sekeisman1275

    sekeisman1275 New Member

    Bogs down uphill

    I just bought a 49cc Chinese bicycle engine and I have it mounted to the frame of a Schwinn mountain bike. It is running well, but I can't seem to figure out if I have the air/fuel mixture figured out properly. I have adjusted the clip on the pin at every level and noticed a difference for each setting. I currently have it set to the leanest clip setting (1st notch) and it runs fairly well.

    I know that most people say that it runs best on the second notch, but when I set it to 2nd notch the engine would bog down when I would rev the throttle quickly, and it would also 4-stroke at 80% throttle. I have taken the whole carburetor apart and checked to make sure the float was level.

    The problem that I am having is that my bike has very little power when it is going up any incline at all. It does great on level ground and down-hill, but when I am facing any kind of up-hill grade it slows down significantly. I can have the throttle at 100% and I cannot feel it rev up. While going uphill it either revs down (if the hill is serious) or it stays at a mid rev sound (I'm sorry I don't know how to explain it with proper terms). Is this normal for the bike to suck so much uphill, or should I be getting some acceleration uphill on small hills? Thank you for any advice and assistance.
    Last edited by a moderator: Dec 15, 2015
  14. happycheapskate

    happycheapskate Active Member

    I have a 49cc, with a 36 tooth cog, on a heavy beach bike. It will pull my 140lb butt and some cargo up overpasses and similar grades, as long as it was moving over 20 when I got there, not much grunt under 20mph with the small cog.

    It pretty much sucked until break-in. You'll know when it gets there.
  15. SdCruizer

    SdCruizer Member

    heres a stupid idea, but check the plug gap
    my stock came set at 50 and while it worked just fine I put in a new plug after break in and copied the gap at 50 and it struggled up hills, but flat ground it was fine

    maybe your plug is fouling who knows but check it out

    any changes your making with the needle may change once you break in and change the mixture
    whats your ratio at now?
    Last edited by a moderator: Dec 15, 2015
  16. sekeisman1275

    sekeisman1275 New Member

    So I changed my plug wire and my spark plug. I am using a NGK bp5hs plug with a gap of .030 but it seems that my bike is still having the same problems.

    Additionally, after I warm up the engine and have it sitting still at an idle if I try to crank the throttle to get it to rev up from a stand still it totally kills the engine. I will twist the throttle grip at an idle and It sounds like it bogs really low and then it just dies. I have tried this on every needle setting and it seems to have less problems when the needle is at the 1st notch (top position), but it isn't any significant difference.

    Also, my ratio on oil/gas is 16:1 because it is the second tank of gas I'm running through.
    I am not getting any kind of good mpg by the way. I went through my first tank and only got like 40-50 miles on the whole tank.
  17. bms420

    bms420 New Member

    no matter what I try I can't get mines to stop 4stroking.... I have the C clip at the very top less four stroking but still there even more the lower I go..... Help!
  18. happycheapskate

    happycheapskate Active Member

    Have you tried checking your fuel filter? (disconnect the line from the carb, into a jug, and see if it flows freely.) Also a good time to see if your fuel cap is venting. (do the same thing, if it is not flowing, and open the gas cap a little. If flow speeds up rapidly, its the cap). Be safe. Don't spill gas on the engine or ignition, and be ready to plug/crimp the fuel line, move it to a gas can, or shut off the fuel valve.

    Using thick oil or a lot of oil can clog up some fuel filters, especially paper ones not made for gravity feed lines or for mix-fuel.

  19. happycheapskate

    happycheapskate Active Member

    Try another spark plug, too, esp a known good one with a lesser gap. I ran a champion lawnmower plug for a while, on a happytime. It ran ok once the engine was good and warmed up, then ran a little hot, but the engine sputtered and was temperamental until then.
  20. tooljunkie

    tooljunkie Member

    i resized my carb jet from a 70 (.028") down to a 74(.0225").
    still four stroking,needle is on top groove.
    i put the jet into a cordless drill,and held the number drill in my pin vise.drilled out easily.
    my pin vise is a tip drill used for cleaning cutting torch tips.