Lost a lot of power

Discussion in '2-Stroke Engines' started by justin.fiveash, Aug 7, 2014.

  1. justin.fiveash

    justin.fiveash New Member

    My bike was running great with the stock carb. I received a performance carb in mail and changed it out. Now it's running like ****. Any advise?

  2. crassius

    crassius Well-Known Member

    I hate these 'performance' carbs. Few work well on an unmodified engine & exhaust. Go back to what works.
  3. butre

    butre Well-Known Member

    performance carbs are a supporting mod, not a bolt on for stock engines. you need a better exhaust flow and probably a better intake flow to make any use of the thing
  4. jaguar

    jaguar Well-Known Member

    make sure the float is even with the carbs horizontal when just closing the input needle.
    too low and the bike runs too lean at idle. too rich and it runs too rich at idle.
    too lean or rich may mean it won't start at all.
    Once you get it idling then you have to adjust the needle height for clean running at middle RPM and then adjust the main jet size for clean running at top RPM. That is true of all carburetors, not just yours.
  5. Fabian

    Fabian Well-Known Member

    The standard NT carburettor (when jetted correctly) works as well as any of the "so called" performance carburettors.

    The only meaningful improvement over a float style carburettor is a Walbro style diaphragm carburettor, though for the same venturi size it will not make any more power, because the laws of physics dictate how much air can be moved through a given internal venturi diameter.
  6. justin.fiveash

    justin.fiveash New Member

    Yup. I put the NT back on and jetted it. Took about 5 hrs to get it right, but I finally got it. I love this bike!
  7. Fabian

    Fabian Well-Known Member


    A properly jetted standard NT carburettor is surprisingly reliable and works surprisingly well.
  8. Fabian

    Fabian Well-Known Member

    The only thing better than the standard setup is a Walbro style diaphragm carburettor; allowing ease of tuning when compared to a float style carburettor, such as the NT.
    The Wabro has external Hi and Low jetting screws so there is no mess as compared to the standard float carburettor; requiring the fuel bowl to be removed 30 times to change main jet sizes when optimising the air/fuel ratio.

    Once you have installed a diaphragm carburettor (with thermal isolation spacers) you will never go back to a float style carburettor, not just for the ease of jetting but for the fact that they don't suffer air or fuel leaks.
  9. HeadSmess

    HeadSmess Well-Known Member

    i been thinking of making a separate bowl for the NT... with a nice simple adjustable main jet hooked up to the existing straw via a hose :)

    it will be necessary when i actually finish this dyno stand...

    whaaaa? they do it on lil outboard engines, mine even has adjustable high AND low!

    theres one performance carb out there, the "red filter" one...only difference i can see between it and the stock NT is that it has a fuel tap? of course, it isnt the only "performance" carb out there.

    everyone is agreed. stick to the NT :) or nitto, depending which label you choose to look at?
  10. crassius

    crassius Well-Known Member

    yeah, I recall when the Kendik pumpers came out in the 70s - beat mikuni all the hell
  11. HeadSmess

    HeadSmess Well-Known Member

    :iagree: they also dont briefly DIE when you hit large bumps, due to the fuel sloshing round and exposing the jet... i HATE that!

    but i still use the floaters...
  12. jaguar

    jaguar Well-Known Member

    a standard NT carburettor is surprisingly unreliable and works horrible as it has no idle circuit and if you adjust it for proper running at high speed then it is off at mid throttle.
    Anyone that is happy with a NT has never had a properly tuned 2 stroke.
  13. Fabian

    Fabian Well-Known Member

  14. HeadSmess

    HeadSmess Well-Known Member

    *speed reads through new link*

    that, my dear sir, is exactly what i have in mind, except far simpler...and stuck on the stock old nt carb.

    bit of profile milling to some alloy, to replace the bowl. reminding me i need windows again cus i cant get certain software to work on linux....grrr! i have about 8 jobs lined up, waiting for me to get a new PC for the mill...

    a right angle junction, M5 up top for the nt straw, to REPLACE the main jet entirely, simple needle valve and a fuel nipple. much like this thing...


    and then the bowl, which still requires a float, and to stay at the same level, hanging off the side...knowing me, with either tek screws or zip ties. or wire cus zip ties cost money!

    simply adjust as suits the load/speed. i did say its mainly for the dyno testing ;) but cnc does make for mass manufacturing processes...as mass as a guy using scrap can get, at least... scored with one job, i have a couple of kg of 65X16X "whatever length it is" billet kicking round now...

    that link included a link to the hijet! now im off on a tangent...i need a gearbox that will fit a daihatsu charade 800cc, but is for a rear wheel drive car, not the FWD transaxle.... hijet, i believe it should be...hard to find :(
    Last edited: Aug 9, 2014
  15. HeadSmess

    HeadSmess Well-Known Member

    please explain why this idle circuit is so important on a POS engine that can barely make 2hp and most people are perfectly content with it at WOT? 99% of us dont use the mids...its either idling (NT deals with that fairly well IMHO) or we're attempting to pull the nipple off the cable...why the need for the "mid range"?

    oh. right. because with 2hp on demand, one needs to be very careful with how they apply the throttle...my bad :eek:

    now, lets talk about needle tapers, and changing the angle on the bottom of the slide, or even, if one dares, changing the needle jet orifice size... all small modifications that are quite easily made.

    though, i do agree....theres NO WAY i would stick something like an NT on to a real 2 stroke, like a good old kx, cr, or yz 80... then, they need some throttle control, despite being lil 80's. gets even worse as we go up the scale into the 250 or 500 sizes... its a brave man (or girl, i know some crazy ones) that will go WOT on a RM250...

    a lawnmower style carb for a lawnmower style engine.... suits most of us ;)

    the bandsaws just stopped! back to the welder!
  16. justin.fiveash

    justin.fiveash New Member

    I'm really happy with my NT, and I got that thing tuned perfectly. There is a little rattle in the mids but it's almost unnoticeable. I am very happy with this machine!
  17. jaguar

    jaguar Well-Known Member

    Justin, what if that little rattle is detonation and you think everything is great till one day it just dies and upon diasassembly/inspection you see a hole in the top of the piston? Then will you still be happy with the NT? No, because you can't separately adjust it for all three throttle ranges.
    I believe in doing things right and for all of you in believe things are fine if they aren't bothering you well that is your own bizarro world and you can just have it.
  18. Fabian

    Fabian Well-Known Member

    It's highly unlikely that part throttle detonation would ever be able to put a hole in the piston or even damage an engine making less than 2 horsepower at the rpm these things run at.

    Because of their low power, they have effectively 2 throttle positions: idle and wide open.
    So long as the engine is correctly jetted for wide open throttle, every other throttle position will work itself out, because you just don't spend any meaningful time there.

    The rattle in the mid range is most likely piston slap.
  19. Nutsandbolts

    Nutsandbolts New Member

    hey everybody my 80cc motorised bike would start then turn off

    my 80cc bike will start then turn off i pedal down hill and i relased the clutch, it goes for 2 seconds then turns off i need help please anyone :ack2:
  20. Fabian

    Fabian Well-Known Member

    @ Nutsandbolts

    Where abouts in Australia are you located?