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...
    Dustmonkey likes this.