Updated HT Carb?

Discussion in '2-Stroke Engines' started by Skyliner70cc, Oct 4, 2008.

  1. Skyliner70cc

    Skyliner70cc Active Member

    Does anybody know a vendor who sells the updated happy time carbs? I've got an engine that is being a little finnicky (did I spell that right) and is running way too rich at idle to mid-range.


    PS Weblinks would be appreciated.

  2. arceeguy

    arceeguy Active Member

    Skyliner -

    Try lowering the metering needle (raising the clip) one or two notches, along with raising the float level (by bending the tangs) about 1mm.

    Lowering the metering needle will lean out your idle/low mixture for better throttle response, and raising the float level slightly will prevent leaning out at mid/open throttle conditions. It's a pain to get them "dialed in" with this method, but it is worth the effort with better performance and fuel economy.
  3. Skyliner70cc

    Skyliner70cc Active Member

    I've tried all of those tricks on other bikes I've built, but this engine is VERY tempermental. Since I build and sell, its important that my customers get a great running engine.
    I live at 6600 feet and the stock idle mixture circuit is just too rich for this engine. Previous builds were rich at idle but engine response as you accelerated off line was acceptable, this one stumbles too much. Luck of the draw ;-)
  4. arceeguy

    arceeguy Active Member

    I'm on build #5 now, and haven't run into a carb that was that so far out of tolerance that I couldn't get it to run right. I usually run them slobbery rich for the first quart (25 miles) to get them past the critical first few miles of break-in before they go out the door. Then I fine tune the carb the best I can, making sure the engine isn't too lean at WOT. I've been recommending a 32:1 fuel/oil ratio and they are all still chugging away.

    A "pit bike" carb, like this one:
    Will probably work if you can weld a flange to the intake on the engine. They have removable jets for fine tuning. (keihin jets fit) They feature an adjustable air bleed a idle, so you can fine tune idle mixture but you need to get the pilot jet in the ballpark first.
  5. I would not recommend the carb posted above. The Hondas that they reference are four stroke engines. That carb is for a four stroke. Be careful that you get a carb for a two stroke, as it will be much easier to jet. You look in ebay you can find 18mm mikuni carbs that have the clamp mount. I got one from a 80cc Yamaha, but have seen tham also listed for kx65 Kawasakis.

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