Carby Carb comparison

Discussion in '2-Stroke Engines' started by Steve Best, Jul 16, 2016.

  1. Steve Best

    Steve Best Well-Known Member

    I've collected some parts and now have a selection of carbs. NT, CNS HiPo and Dellorto clones (RT).
    Both my engines are quite close to stock now so anything I look into will be good for new members.

    My motors are a 2015 66cc Grubee GT5A with a direct drive 44t sprocket on a 26" tired Mountain Bike,
    and 2013(?) 48cc Grube GT2A with a jackshaft shifter kit on lightweight 26" frame.
    Engine mods on both motors are limited to head mods, squish band home machined in at 0.030" gap.

    I've had great luck with the stock NT carb. I have 4 of them and all have worked well.
    No size written on the jets that I could see but all work well, slightly on the rich side, so I dropped the float level and needle and verified with a plug chop. The NT really needs the choke and tickler to get started. Cold blooded beast, and worse once I dropped the float.

    On the stock 66cc motor I get a top speed of about 40-45 kph but the NT carb was capable of 66kph on a moderately ported cylinder and the same squishband head. This is about 10,000 rpm and may be as high as you dare spin these motors. I had the end of a wristpin circlip break off, no doubt from the rpm stress. This scored the ported cylinder which is why I have a stock cylinder on again. With hundreds of kms in the 8000-10,000 rpm range, my 66cc motor has loosened up at the rod big end bearing, it is noisy and I can barely feel clearance which is normally a sign to replace.

    My verdict for the NT? Good reliable carb. Recommend it.
    This is the place to start. Only a main jet and needle to tune and all I have work well out of the box.

    So now the CNS. It comes with a bad reputation for tunability.
    I put it on the GT2A with a thumb throttle and a lever on the handle bar for choke. (More cables!)
    It started first kick and dead steady idle. Wow! Much better idle and starting than the NT.
    No need for the choke in warm weather. choke and kick once in cold, immediately choke off.
    Idle must be set rich but it works excellent so I'm gonna leave it alone.
    Test run indicates a tan plug so no need to rejet. More to come...

  2. Hopefully I can tap into your experience with these carbs. I'm wondering what your recommendation would be? I to have the 2015 Skyhawk Gta5 on a 26" Bike. What would your ultimate recommendation be with buying a carb?? If you could provide the name of the carb and where to buy it that'd be great!!
  3. butre

    butre Well-Known Member

    I use a PZ19 carburetor on my regular engines, currently building a 98cc engine using a 30mm oko
  4. Would it work on a 66cc?

    Attached Files:

  5. butre

    butre Well-Known Member

    you need to make your own mounting adapter. mines a fender washer with holes drilled to fit the carburetor flange wirh a section of pipe that fits snugly over the spigot mount on my reed valve. you should be able to do the same with the stock intake plenum, though there will be some restriction as the inside diameter is only 16.5 mm if I recall. alternatively you may be able to drill new holes in the carb to match the spacing on your motor, but I'm not sure if that'll work for you.
  6. Ok I appreciate the suggestion and the price range is great (I'm looking for a decent carb below $30) but I prefer a bolt on ready to go carb, would you know of a decent one in my price range?
  7. Steve Best

    Steve Best Well-Known Member

    Carl, after playing with many others, I still feel the stock NT carb is surprisingly capable. It is not the weak link in the power chain, its lack of adjustment is a blessing and will run a single speed bike up to 40mph with only cylinder and head mods. Swapping to a 19mm didn't improve any engine I've built yet.
  8. Ok thanks Steve. I'm surprised it works just as well due to the restricted air flow but if its not an issue I'll stay with that one.
  9. Frankenstein

    Frankenstein Well-Known Member

    It's not restricted as far as air flow goes, it's the size that these engines handle without a problem, going too big makes for the problem that air velocity through the throat gets so low it can't suck up gas on the way, you'd need a bigger pump (engine) to work a bigger carb.

    Can't say I've seen any engine with a larger intake than it did the exhaust opening, so it's unlikely you'll ever need a carb with a throat the same size as your header.. I know the same 19mm carb can be used from anything with a 50cc motor to a 110, so an 18 is going to handle any Chinese happy hour motor.

    If I want a new Cns carburetor with the hot markup on the price Tage since people try to make money by selling this as a speed upgrade I would pick up this here at the fair, cool price of 16 bucks, you'll need a compatible air filter and probably need to make a spacer to fit the carb to your 18mm intake (or buy a 19mm which I think you can do.)

    That carb, listed for a pw80 motor, is the same exact thing sold as a Cns carb, and as well as a Cy80 Honda carb, and the list will go on if you search for it, as I said in the past this carburetor design has been around for a while so whoever sells them finds out what they can use it for, and how much it can be marketed at, apparently in the motorized bike realm that carb is worth more than it would if it was being installed on a Yamaha instead...

    So there you go folks, a "high performance race carb" at the stock carburetor price, learn to tune it and ride.
    Steve Best likes this.
  10. Well I was looking at previous threads and it looks as though several people believe the stock NT carb works just fine or just as good as the other carbs out there, especially if someone isn't racing their MB which I'm not.

    I am currently looking because the previous clone carb I purchased off of eBay leaked due to a poor plastic molding of the cup, I fixed that with gasket seal and the leak stopped. Now I have an issue with the throttle cable being to long, & therefor to loose, & I have no clue as how to make the cable tighter. There's the little nubs on each end so I know they can not be cut so how in the hell do you tighten up the throttle cable?? Please don't tell me I have no choice but to wait on a new one.
  11. Frankenstein

    Frankenstein Well-Known Member

    I couldn't tell you unless I physically was looking at the parts and saw how long it was, from here I can't tell you if you can adjust it out with the 2 barrel adjusters.

    You know that little noodle that sticks out the top of the carb? Well I have plenty of noodle like things and the related barrel adjusters that go with them. I had my Dellorto at one point and I ended up with a too long cable so I found a tiny barrel that would fit the end of the the carb barrel, and just removed what material I had to from the barrels so the length was spot on. The picture below is the same idea but with brake lever adjusters instead of carburetor parts. If you looked around your odd parts long enough you might find something, or at the very least use a small Allen head bolt and the appropriate sized drill bits to make a spacer of some sort. 20170711_182500.jpg
    FurryOnTheInside likes this.
  12. Well I'll take a picture when I get home from work if need be. I asked my son to google it and see what he could find and hopefully fix it but he is almost as lazy as me so we'll see if he made any progress.
  13. Do you know what that part is called and if certain ones will do a better job of tightening the cable then other ones?? I'll go out and buy one now at Lowe's or wherever if that's possible??
  14. Frankenstein

    Frankenstein Well-Known Member

    I don't know what it's called but the object you use only needs to do a small simple job, and the lack of strain in that area means it could even be a simple piece of plastic. I would bet that if you had time to scour all the miscellaneous odds and ends that you can find at a hardware store you'd stumble across something that could work. If I was desperate I could fill a small paper cylinder with jb weld and let it cure, then drill that out and shape to my needs. Really the options are endless once you move outside of buying and into making what you need.
  15. Crisco

    Crisco Member

    Dude... Check out this crazy place called YouTube...!!! There's heaps of easy ways to shorten a cable and get a reliable barrel end to suit..
  16. I never knew you could go to this crazy place called YouTube to search for the names of objects!! When I go to this crazy place do I put in the search field "What is the name of the thing at the end of the throttle cable?" and YouTube will show me what, a video of someone telling me what the name is?? I learn something new every day.
  17. Frankenstein

    Frankenstein Well-Known Member

    Cable nut?
  18. I searched the garage and between numerous parts I was able to make it work but I was forced to use my thumb throttle which I hate. So after messing around for about 3 and stripping out my new throttle I finally have everything running but its not running that good.
  19. HumanPerson

    HumanPerson Active Member

  20. HumanPerson likes this.