Carby what are the advantages /disadvantges of getting the "speed" carb?

Discussion in '2-Stroke Engines' started by motorpsycho, Aug 14, 2010.

  1. motorpsycho

    motorpsycho Active Member

    I am considering buying the nt "speed" carb for my 80 c.c. h.t. 2 stroke. what are the advantages of having this carb? easier / more tuning ablilties? increased engine power?
    or would re-jetting my stock nt carb for more power be easier and cheaper to do?
    I have already ordered jeys for my nt carb, but now i am thinking that maybe the "speed" carb will give me more tuneability and MAYBE a little more power.
    so is the speed carb. worth buying?
    or, would the better carb be the cns "racing" carb?
    I don't really care for the handlebar mounted choke lever tho, but if the carb is better, i'll have to deal with it.
    Last edited: Aug 14, 2010

  2. GearNut

    GearNut Active Member

    From what little I know about them, both the nt speed and the cns have a larger venturi that is better suited to a 66/80cc engine. Someday I might get one and learn more about it.
    The stock kit carbs are all sized for 49cc, regardless of engine size.
  3. I will problem be ordering one today or tomorrow. Once it gets in I could let you know if you like.

    Its in Canada so it should be here in only a couple of days.
  4. motorpsycho

    motorpsycho Active Member

    i went ahead and ordered a cns carb. last night,
    so we'll see how it is once i get it.
  5. Skyliner70cc

    Skyliner70cc Active Member

    Can you post a link of where you purchased it from? This way if it works for you, I'll get one too. I know many vendors sell 'em but with so many players in China on the HT bandwagon, I want to make sure I don't get a lemon.
  6. motorpsycho

    motorpsycho Active Member

    yes i can do that. I will have to see how the carb is when i get it.
    I noticed on my newest build (a 66 c.c. h.t.) now that i reduced the gas-oil ratio from 16:1 - 24:1, it runs a whole lot better. i was running the 16:1 for break in, but someone suggested that 16:1 is too much i dropped it to about 24:1.
    but now that i have some break in time on the engine, and i'm running a slightly less oily mix...the engine runs a whole lot better, but it seems that in the mid-top end rpms, the engine is undercarbureted. I know what it's like when you try to run too small of a carb on an know the power is there, but the carb is not allowing enough air/fuel for the engine to breathe and run like it should.
    I am hoping that the cns carb. takes care of this.
    I ordered a bunch of jets too, so I will have to play around with the cns until I get the engine running it's best. I will start out by seeing what main jet is in the cns before I even bolt it on the engine. I know that my stock carb has a #70 jet in it, and it's a little too rich.
    If the cns has a bigger venturi, that means that it will be pulling more air, so if it has a #70 jet too, it may be just fine right out of the box.
    I will not know until I mess with it and see if it's too lean or too rich.
    I do plan on spending some time having to tune the cns carb. and doing jet changes after I get it.
    Last edited: Aug 16, 2010
  7. motorpsycho

    motorpsycho Active Member

    ok, i got the carb. today and got it on.
    it's more than just swapping out one carb for the other (in my case anyway)
    Since i originally shortened my throttle cable, i had to shorten it a little bit more for the new carb. It does come with a new throttle cable, but the ends are the same as the stock cable, so i just used my original since i shortened it to fit my bike already. I also had to replace the clutch cable guide bolt that has the hole in it for the clutch cable to run through because the float bowl would hit the stock cable guide. The carb comes with a shorter clutch cable guide bolt (or whatever you want to call it) so that was no big deal. The fuel inlet fitting is at the front of the carb angles forward rather than in the center and straight up. My fuel lines(yes, i have 2 lines coming out of my tank) run to a T fitting and then a single line comes out of the T with the shut off valve in it and then to the carb. I had to put on a slightly longer fuel line from the shut off valve, to the carb. The carb is A LOT bigger than the stock carb both externally and internally. the throat of this carb is HUGE compaired to the stock one, the slide is bigger in diameter, the float bowl is bigger, the float is actually like a "real" float set up, and it has a much better mounting clamp that holds it to the intake manifold. The thumb operated clutch lever with cable is a joke. the cable only has one end with a "barb" on it. the other end is just cable. the thumb lever requires a "barb" like the size of the one that is in the throttle handle assembly for the cable to stay in it. the choke itself requires a small "barb" like the one on the throttle cable that hooks to the slide. so there is no way to hook the cable to the thumb lever unless i make my own "barb". so for now i left that cable off and the choke is always closed because it has a spring holding it closed. with the cable hooked up, you pull it and the choke moves up. i wouldn't say that it's a choke tho really, it's more like an air bleed valve. (open it to choke, close it for no choke) I never needed the choke with my stock carb so i will leave the cable off because it started right up without using the choke as it did before with the stock carb.
    there is an air/fuel adjustment screw and an idle screw. there are 2 vent pipes on top of the float bowl that must remain open. there is another short tube that comes out of the carb body in the rear and it goes into the carb throat on the intake side, this tube is not blocked off, and unless you plug it, it will have a massive vaccum leak because it just sucks air. I used a rubber vaccum port plug to cap it off.
    I have not yet played with the jet needle clip setting yet or the main jet. I did take the float bowl off to see if the main jet was numbered, but there is no number on it, so i have no idea what size main jet is in it. the float set up is more like one that you would find in a motorcycle carb. MUCH better than the plastic hollow floating disk set up in the stock carbs.
    i got it running and it fired right up without making any adjustments to the carb at all. the idle was set perfect. i took it for a ride and it seemed a bit rich from idle- 1/2 throttle. so i played with the air-fuel mixture screw and got it running good. but it seems to be a bit still rich at wot, so i will have to play with the main jet. i have a bunch of jets ranging from #60 through 74, but i have no idea where to start. I don't want to start with a jet that is too lean right away or one that is too rich either, without knowing what jet is in it now, it's tough to make a decision on what jet i shoud stick in there in place of it so i can establish a starting point by knowing the jet #.
    so if it is too rich right now, and i put a #68 jet in it, what if the stock jet is a #74 (for example). dropping from 74 to 68 would be a drastic change and it would probably be way too lean. but without knowing the stock jet size, this is going to be tough. i guess i could take the stock jet out and put it side by side with the other jets and eyeball the hole that's in it, but that wouldn't be accurate at all because the hole sizes are so close in size.

    by the way, i could not get an actual cns carb because it seems like every place that offers them is out of stock. so i took a chance and got one from boygofast. it's labled as a high performance carb, and it looks identical to the cns carb. The name on it is wabrow (not to be confused with WALBRO).
    but man right out of the box it made a huge difference in the way my engine runs, it revs faster, and has more pulling power. the engine just seems happier with this bigger carb.
    no joke, this carb is about the same size (externally anyway) as the one that is on my Kawaski 100 enduro, and it's design looks almost identical to the kawasaki carb.
    it also looks identical to the pics of the cns carb that is various vendors sites. It's very high quality and not cheaply made(like the stock carbs.) it's beefy and it is well built.
    I know, it's probably a generic version of the cns, but it was cheaper, it looks the same, does not look cheaply made, and i got it in 3 days. ordered it on sunday, got it on wed.
    so far so really woke my engine up.
    Last edited: Aug 18, 2010
  8. GearNut

    GearNut Active Member

    Thank you very much for the up-date and initial review!
    Last week I was surfing the internet trying to find a similar carburetor currently used on a major name brand motorcycle. I was intent on finding an exploded view, and perhaps a tuning guide and alternative jet sizes for sale that I could share with this site.
    All I found was a bunch of pictures, but nothing detail oriented.
    Kawasaki, Yamaha, and I think it was Polaris all have similar carburetors, but not identical ones.

    If you could, please give us a blow by blow account of how this carb works out for you, and all the "juicy" tuning details.
  9. skrufryder

    skrufryder Member

    oh yeah the "race carb is awsome you can realy fine tune the engine here in seattle the weater changes drasticly from day to day so having a mixture screw makes a great differnce.
  10. motorpsycho

    motorpsycho Active Member

    yep...the carb is a HUGE upgrade. you can truly fine tune it with the air fuel adjustment screw.
    it is a bit rich tho right out of the box, so i will have to change the main jet (ordered a bunch of different dellorto jets from sbp).
    I'm just not sure what jet is in the carb. rightout of the box because there is no number stamped on it.
    I have not done anything with the carb, since i installed it last week.
    but right out of the box the engine fired up, and ran great...just a little on the rich side at w.o.t.
    i think i have jet sizes ranging from #60 all the way to #78....i got every jet that s.b.p. has on their site.
  11. Fletch

    Fletch Member

    I was using that carb and it was great. I had a HD filter on it from SBP which I don't recommend because it ended up breaking the threads out of the carb (because the screws are so long).

    So I took the barrel slide and jet out of the speed carb and put it into the old NT carb. Is this going to be a problem? I haven't ran it to check the plug yet, but the speed carb gets more air as well as having the larger barrel and jet. I think it has a larger air intake as well as the larger air filter. I just used the black NT filter.

    Would someone explain to me the different between replacing just the jet and replacing the entire barrel slide? If I'm running too rich, will adjusting the needle work in this case, or do I need to get more air to the carb by maybe opening up the air intake hole?
  12. Chimpo

    Chimpo New Member


    Do you have a link to the carb that you reviewed?
  13. Fletch

    Fletch Member

  14. DuctTapedGoat

    DuctTapedGoat Member

    From what I've heard of the differences between NT and NT Speed is that the floatbowl is bigger. The CNS carbs from my experience don't have a stock air/fuel mix screw, but they have two vertical floats. I'm not a fan of the cabled choke either on CNS. I wish I had an NT Speed to compare by hands on with the NT.
  15. Fletch

    Fletch Member

    I had them side by side today and spent the afternoon turning an NT into an NT Speed. I can tell you the difference now for sure.

    The throttle slide is a tiny bit larger on the Speed (won't fit the NT).

    The throttle barrel is wider, as is the main jet.

    The air intake and output holes are 3mm wider.

    I bored out the air intake hole all the way through, and swapped the throttle barrel and main jet from the Speed, as well as the needle which is a little wider and has less of a point. I kept the old throttle slide, and put on the ugly red Speed air filter. I started the engine to see if it would work because I did some other things to the engine, but I didn't ride it.

    Tomorrow I'll ride it and see how it is running and if the air/fuel needs to be adjusted.

    The bowl might be a tiny bit deeper but I forgot to measure. It's the same width.

    I think the CNS is the biggest piece of garbage ever. I wasted so much money on 3 of those and billet intakes. They all broke, and I have a large ziplock freezer bag full of cns carbs and tons of extra parts to them. I'm going to organize everything one day and to take a pic and try to get rid of it all.

    TAYLOR MADE New Member

    The bigger carb getes you off the line faster but does not give you more top speed.
    It also uses about twice the fuel..
    If you have an exp. chamber the bigger carb makes the bike A LOT louder,sounds like a dirt bike...
    You can also shorten the 'handel bar mounted clutch leaver' to mount under the seat on the frame ,so there is one less cable running uo to your handle bars
  17. Fletch

    Fletch Member

    The problem is the **** thing vibrates off the intake manifold. The metal they use is really weak. I bought 2 ported intakes for the CNS and 2 different carbs broke off completely where they clamp on the intake. I would avoid the ported billet intakes for the CNS, and if you are going to use a CNS, don't take it on and off a lot. I would ****-near glue the thing on the intake. Blue RTV wasn't strong enough for me. The NT/speed carbs have a smaller output diameter and tighten down on the intake MUCH better. The CNS output is too wide and the carb itself too heavy (the old one's at least- don't know about the new 2nd generation). Add vibration and they brake off or fall off.
  18. DuctTapedGoat

    DuctTapedGoat Member

    The red speed cover wouldn't be so bad if it weren't for the fact it just reminds me of the CNS carb.

    Well, like I said, I don't have an NT speed, but I was looking at them only last night, and noticed that they were saying that you needed to modify the clutch locker bolt thing on the motor to lower it to compensate for the deeper float bowl. Or correct me if I'm thinking of a different carb, now I'm not absolutely certain!


    2nd gen is still bulky, untunable, heavy garbage.
  19. Fletch

    Fletch Member

    The only time you need to cut threads on or shorten the clutch bolt is if you use a ported billet intake. I'm guessing that's what you were reading about? There's no way that the bowl is any deeper than a few millimeters (if at all). I'll check tomorrow. It's hardly noticeable if there is a difference. The jet size is the main reason for increased performance. For 25$ it's worth it to me though. If it was just a larger jet I would replace it, but the secondary fuel shutoff and wider throat hole (more air), make it worth it. Plus it seems to fasten on better and has a little clip that helps tighten it down by holding that square nut in place.
  20. DuctTapedGoat

    DuctTapedGoat Member