HT Carb needle variance

Discussion in '2-Stroke Engines' started by Flapdoodle, Mar 27, 2009.

  1. Flapdoodle

    Flapdoodle Member

    I finally got around to miking the needles on three HT carburetors. One has been in use for 450 miles, the other two unused.

    The one in use is much slimmer (more radical taper) than the other two, and came with the clip second from the top making it even richer. This was the machine I reduced the main jet from .028 to .024 inches and still is a little on the rich side. The clip is now on the top groove.

    The other two needles are identical as far as I can tell and came with the clips on the very top groove.

    We are in a cold snap, but as soon as I can I will measure the factory float level height on all three carbs weather permitting.

  2. Flapdoodle

    Flapdoodle Member

    I measured the float height on the two new carbs measuring from the gasket to the bottom of the float with the carb inverted. I got .772 and .750

    Guessing, I would say it is possible for the distance to get smaller when the kit is bounced around in shipping, but can not get greater.
  3. arceeguy

    arceeguy Active Member

    Remember that the jet needle and the needle jet go together as a pair, so the "slimmer" one may be matched up to a smaller needle jet.

    Are all the carbs from the same factory and supplier? I've found that BGF carbs do not have "NT" cast in the body like the carbs from PKS and Grubee. They all look the same, but maybe there are internal differences? (Just like "HT" engines in general)
  4. Flapdoodle

    Flapdoodle Member

    All three are from BGF. None have any cast-in lettering. Two have a place for a drain, but not drilled and tapped for a plug like the other one.

    Your point is taken about the matching. I will measure the holes the needle fits into next.
  5. Flapdoodle

    Flapdoodle Member

    The two carbs with fatter needle tapers mate to needle jet hole with a #44 size, and the one with a more drastic taper a loose #45 hole. In this case, I would NOT say the needles are matched to the jets they fit into. But it does explain why it was very rich out of the box.
  6. arceeguy

    arceeguy Active Member

    Very good info - thanks!

    I guess we can safely say that the carbs are "pot luck" as far as tuning advice because of the variations.

    I've seen some variations of NT style carbs come across my workbench. Some had the drain cast in the bowl, but no hole drilled and tapped, others had the drain screw installed - and some didn't even have the boss cast in the bowl.

    For the 66cc (80cc) engines, I have needed to raise the clip on the jet needle to the highest position to lean out the low-mid range, and drill the main jet to fatten up the top end. But this was on a pallet of engines that were identical. As they say - your mileage may vary!