Carby rejetting info Needed

Discussion in '2-Stroke Engines' started by wan37, Apr 7, 2012.

  1. wan37

    wan37 Member

    I have a nt carb with a performance air filter and it's running to lean.I also have the c clip all the way down.I don't think it has any air leaks either.So what jets should I buy to make it run richer.Thanks

  2. vermhot

    vermhot Member

    Before you do that ,look at your oil fuel mix ratio!! You might have it to lean to start with !!
  3. wan37

    wan37 Member

    I'm running 32 to 1 ratio .I can't see that being the problem.I have read a lot of post and can't remember ware to look for my answer to my question.So anybody help me out here?What size jets to make it richer on a nt carb.
  4. motorpsycho

    motorpsycho Active Member

    well, no 2 carbs will be jetted the same as in "what jet should i use?"
    the best thing to do really is to get a variety of jets and try each one in progession until i runs good.
    what works for one, may not work for another.
    start with a low jet # (like 68 for example). get the engine warm and ride it through the entire throttle range, low speed,. mid speed and top speed.
    if it bogs down at w.o.t., chances are, that jet is too lean. also check the plug color.
    then work your way up in jet sizes, one jet at a time until it runs perfect through the entire rpm range, and your plug is a nice tan color.
    it can take a few hours, or it can take 5 minutes in some cases.
    the air temp, humidity where you live and your elevation also come into play.
    here's what i did (which may not work for you).
    I removed the stock nt jet, and had no idea what size it was...assumed it was a 70.
    I stuck a 68 in, and rode it.
    the 68 was way too lean. so i jumped up to a 72. it ran a lot better. then i went to a 74 and that was a bit too rich, so i dropped back down to the 72.
    there have been a lot of people who say that the stock (presumably 70) jet is too rich and they end up leaning it out with a smaller jet.
    well, i had to do the opposite and richen mine up with a 72 (assuming that the stock jet was a 70). my ran like it was jetted too lean with the stock jet.
    it's a trial and error thing, and remember to keep your stock jet set aside from other jets because you can always throw it back in and start over of you get confused.
    if you buy aftermarket jets, normally they are marked with their sizes, but the stock nt jet will not be marked with it's size.
  5. wan37

    wan37 Member

    Well motor thanks the plug is reading too lean and its has a hard to start after it sits a while you have to give it some throttle to start it and it final starts after about the third or forth try.I have change the needle setting all of them.No help either.So I know it needs to be richer because of the plug and the performance at full throttle.Also if some one would tell me how too make it start better that would help.
  6. HeadSmess

    HeadSmess Well-Known Member

    go up a jet size. will fix idle and top end, hopefully... being a 1 jet system, the main affects everything!

    i dont know whats so hard about buying a set of these>>>

    and a pin vice/chuck>>>

    and a soldering iron if you go too big :rolleyes7: >>>

    the plug says its too lean. full throttle says its too lean. get pro-active man!
    Last edited: Apr 10, 2012
  7. wan37

    wan37 Member

    Thanks headsmess.I had a blank spot in my head,to go up or down with jet size.So you just told me.
  8. Fabian

    Fabian Well-Known Member

    Every engine seems to have slightly different jetting requirements as standard, but once throwing in accessory options like billet intake tubes, modified exhaust systems, modified intake and exhaust ports and transfer ports, the fueling requirements will change.

    Next up is air density, either with temperature or altitude as these factors have an effect on jetting requirements.

    There is no single bullet theory as far as jet size with so many variables at play. No one can tell you the correct jet size as your engine is unique due to the manufacturing differences with Happy Time engines.

    Ideally you want a fast response exhaust temperature gauge on your bike to assist tuning the engine in conjunction with visual spark plug analysis.

    Two stroke tuning can be both simple and complex at the same time but having a fast response EGT gauge helps to make things a little easier and verifies you're heading in the right direction.

    Send me a PM and i'll send you a link for my EGT setup on my bike.