What type of Jet do I need? CVK Carb

Discussion in 'Performance Mods' started by RocketPenguin, Aug 7, 2016.

  1. RocketPenguin

    RocketPenguin New Member

    To start off, I am a complete n00b to this forum, and to 4 stroke scooter engines, as well as modding. I do, however, have a good understanding of mechanics, the way engines work, and have worked on other motorized projects before.

    My uncle recently gave me his Wildfire WFH50-S2 scooter. Heavily souped, the scooter/moped has an aftermarket, nonrestrictive exhaust on it, a "Racing" CDI (with a full automobile ignition coil), and a larger rear tire. He gave a "Racing" filter with it (The cone shaped kind), and said I could put it on if I wanted to (He didn't, because the diameter of the filter was different than the carb's intake). He gave the scooter to me in a semi-complete manner, as in, a few things had to be put back for it to run correctly One of which was the stock/OEM air filter/box. I soon come to find out, that the cheap chinese mounting tabs on it had broken off.
    Well, I guess it's time to swap air filters.
    So using a part from the old box (The pipe), I managed to put the racing filter on with an airtight seal.
    Then I take it for a spin, and find out it no longer runs as well as it used to. (I tried it once with the old box, and it ran without problem.)
    At idle, there is no problem. At low-medium throttle, no problem. But, when I get to the upper-medium and high throttle/WOP, the engine suddenly bogs down. It accelerates, then bogs down, accelerates, bogs down, etc.
    After a bit of reading and thinking, the only thought I have is that maybe due to the lack of a restrictive box, the fuel ratio must be too lean. So, I get some painters tape, and tape down 80% of the new filter's inlet area.
    Sure enough, the scooter works (almost) as well as it was with the old box (I suspect the ratio is still off, but better than without the tape)
    Then I begin doing some more reading, and come to find that I need to change my main jet (Correct me if i am wrong/if there is another solution). I have never done this before, but I guess it's time to learn.
    I take off the carb, take it apart, and remove the main and pilot jets.

    Then I come across two problems (For all the TL;DR people, this is when you should start reading):
    First off, neither of the jets have any markings whatsoever. No numbers, no logos, nothing.
    Second, I can't find anything specific on the carb, which would point me in the direction of what type of jets I need to buy.

    Here are a few pictures of the unmarked jets:[​IMG]
    (http://imgur.com/a/F8ixf)
    The first picture, from top to bottom, is unmarked Pilot jet, unmarked Main Jet, and the body/housing the main jet screws into. Second picture is just the main jet.
    the dimensions of the main jet are:
    OVERALL LENGTH = 7mm
    HEAD DIAMETER = 5mm
    THREAD MAJOR DIAMETER = 3.9mm
    I found what I believe to be it on this website, however, I would much rather order from a more legit source. That, and I am not even 100% sure that is it. The dimensions match though. What do I need to look for? If I enter those numbers into another search engines, I get a few sketchy ebay links. How would I identify the type of jet I need? And the other thing: I don't know the size of jet I need. Not knowing the size of the current jet I have doesn't help either (Though, a 24awg wire fits into the hole. I don't have any other close gauges to try it with)
    Since I don't know the exact size of my current one, or the size I would need, I don't want to buy them individually (Especially for 7$ + shipping a pop!) I would like to buy a kit, but I haven't found any.
    Same goes for the pilot jet (Do I need to replace that one? I don't have problems at idle/low speeds), found here.
    The most I found on the carb was: [​IMG]
    (http://imgur.com/a/8IpLu)
    With CVK written above it. (For all the people getting physically upset due to the amount of dirt and grime on it, cleaning the entire carb will be the second thing I do tomorrow, right after breakfast.)
    Beyond that, I found no model numbers or anything on it.

    How would I go about identifying the size of the bore, as well as the type of jet I have, as well as the type of jet I need?

    Thanks for the help! If I left anything out, let me know. Any help is appreciated!

    EDIT: From what I am finding, my carb seams to very closely resemble a 139QMB Carb.
     
    Last edited: Aug 7, 2016

  2. Frankfort MB's

    Frankfort MB's Well-Known Member

    You seem to have a stronger grip than I do on jetting;)

    Yes you are lean at WOT (wide open throttle)
    Larger main Jets would fix this problem

    I'm not for sure on what kind of carb your working on???? Or what kind of jets you need???


    (I'm just used to working on 2 stroke Motorbikes but have a good grip on other small engines but I don't know what the parts are, or what they are called:D)

    Is this going on a bicycle or is it just a question about a moped?
     
  3. RocketPenguin

    RocketPenguin New Member

    Thats the problem: I don't have any idea what carb I am working on either, or the jets. In fact, that IS the question, is how to identify both of those.
    It is on a Wildfire WFH50-S2 scooter/moped, and will remain on it. I believe the carb is stock with it, but then again, the scooter is Chinese, and has minimal documentation, if any at all on the carb. The pictures in OP are the only markings on the carb. From what I am finding from pictures, is that it may be a 139QMB or GY6 125-150 carb. Maybe.
     
  4. RocketPenguin

    RocketPenguin New Member

    UPDATE: So, it appears the needle as "Gy50" written on it, and doing a quick google image search, it does appear to be a Gy50 carb. However, I still have not found any jet kits for it.
     
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