Carby Carburetor - help with my grubee skyhawk 2 stroke 66cc

Discussion in '2-Stroke Engines' started by Dyran, Jul 8, 2011.

  1. Dyran

    Dyran New Member

    I've been having my bike for about 3 months now but ive been having a problem with it. when i dont have the choke at least halfway i cant get any power out of the engine, also when i twist the throttle past about 3/4 it sputters and dies. I dont know if its the carb. because ive been messing with it since ive had the bike trying to get it to run right. any solutions to my problem?
    Last edited by a moderator: Jul 10, 2011

  2. Lazieboy

    Lazieboy Member

    Got good spark. your not using the white wire from motor are you? its only for 6v lights. My new grubee kit had CDI hooked up wrong gave some issues. my kit is only a couple of weeks old so it needs to be broke in. I cant get more than 1/2 throttle and it bogs and i dont wanna push it yet. I could feel it when old motor gained power. before it blew a ring.
  3. Dyran

    Dyran New Member

    no im not using the white wire, i followed all the instructions exactly, i actually took the kit apart and switched bikes. i also had one of my friends who has the same engine as me come over and help me build it. now that i think about it, my problem might be the oil to gas ratio, because im still using the 16-1 ratio after having it for 3 months, but im not sure if ive broken it in enough, i try to ride it every day but i lose track of how far ive actually gone.
  4. Lazieboy

    Lazieboy Member


    If u'r gonna get a speedo search this site as not all speedos will work good with engine. it can make them not work or be off. I got a wireless bell from walmart.

    Now my max speed is 20mph kinda comfortability. but with old kit that was broke in it was 32mph top speed on LZ2 build.
  5. Dyran

    Dyran New Member

    What's a speedo?
  6. Al.Fisherman

    Al.Fisherman Active Member

    First check for a vacuum leak, starting at the carburetor. Go buy a "O" ring that will fit into the carburetor where it meets the intake manifold. The cap where the cable is prone to leak.
  7. motorpsycho

    motorpsycho Active Member

    yep i'm guessing that you have an air leak at the carb/intake manifold.
    9 times out of 10, if you have to close the choke to get a warm engine to stay running or accelerate, you have an air leak.

    a normal o-ring (for the carb to intake seal) that you can buy at the hardware store will swell if it comes in contact with gasoline because they are just made out of rubber. if it swells it can become week, break and end up in the engine.
    you need to buy an o-ring that can handle gasoline, and sick bike parts sells them.
  8. Al.Fisherman

    Al.Fisherman Active Member

    NAPA has them, that's where I buy mine.
  9. Old Skool

    Old Skool New Member


    I'm a new guy also and was having the exact same problem with the CNS carburetor. I knew that it was running too lean so I decided to move the adjustment on the needle from #2 to #3. Tinkering with the adjustment screws did not prove to be successful.

    When I opened the carb, I found something that was interesting (to me). There was no gasket on the (top) throttle plate, which opens directly into the throat of the carb. It had to be sucking too much air. I made a small gasket from some gasket material and the carb works much better now. It will now idle and respond to the throttle, without the use of the choke being deployed. You should now be able to make some minor successful adjustments to the two screws on the outside of the carb in order to get it to run correctly.

    BTW - be sure to check the tension on your throttle cable too.

    I went from really aggravated about the CNS carb to "another happy camper" after I installed the gasket. Maybe it wasn't designed to have one, but it sure works better with one.

    Old Skool
  10. Dyran

    Dyran New Member

    One other thing, my engine can idle, but you can't choke it in order to idle. I don't know if that changes anything, but I just thought I'd share that. Thanks for all the help guys and I'm going to buy an o ring as soon as I can.
  11. Basement_Modder

    Basement_Modder New Member

    Check your gaskets for tears. Check your fuel lines for leaks. If needed, tear down the carb and clean it with carb/ brake cleaner. Check the gaskets in there, too. Make sure the piston isn't hitting the spark plug, and re-gap the plug. If desired, open the gap a small bit further, just to ensure a good spark. Be sure all the bolts on your head and crankcase are torqued down to spec, perhaps even a 1/4 lb over, to be sure. (only over-torque with American bolts) Check the idle screw to make sure it idles good. Adjust the other settings on the carb as well, it could be running too lean.

    Hope this helps...
  12. Old Skool

    Old Skool New Member

    I wish you success in getting the engine to run correctly. I have been "monkeying" with carburetors for many years and found that they are commonly the root cause of poor performance. This "new" carb, which seems to be a knockoff of another Jap carb is a little tricky to get right.

    The black O ring has to be thick enough to seal the slotted opening between the mouth of the intake manifold and the back of the carb, which is caused by the method that they use to mount the carb. That is a different part than the white nylon slotted sleeve that fits between the intake throat and the inside of the back of the carb. What happened to the original O ring? Is it stuck inside the back throat of the carb?

    Your former post suggests that the air-to-fuel ratio is much to lean (not enough gas to the percentage of air). You can correct that by either increasing the amount of fuel (or) decreasing the amount of air. Each solution is a different issue, that must be addressed seperately.

    It is always much easier to "show" something, than it is to try to "explain" something on paper. Look carefully at the design and think the problem out. If the intake is sucking air anywhere - other than through the air cleaner - address that issue first. There are several places that the intake system may be pulling in too much air.

    You might also Google "CNS Carburetor" and look at some of the photos, which describe what the various parts look like. I have tried to upload some of my photos into this message and am told that they "exceed the limits of the fourm" for attachments.

    Old Skool
  13. Dyran

    Dyran New Member

    I'm not sure if its the "o" ring or not im about to go take it apart, and go get a new o ring to see if that works, because there may be a leak in it.
  14. Dyran

    Dyran New Member

    I took apart my carb and checked all of the seals, the only one that seemed to have a problem is the one that Old Skool was describing, (the one between the mouth of the intake manifold and the back of the carb), the gasket that came with the engine doesnt seem to be thick enough to make a good seal, so i am going to get another gasket and some gasket sealant, and try to get a better seal.
  15. Old Skool

    Old Skool New Member

    Dyran ~

    Be very careful with this, because you do NOT want to introduce anything in the intake that can be drawn into the engine. If you are referring to the black O ring, I think I would stay away from using gasket sealant on that. You can probably buy a small box of O rings in most hardware stores. Find one that has the correct diameter and as thick as possible. if you are not satisfied with the thickness of the O rings, you can probably also "stack" them together. Don't overdo it!

    After you get the carb "buttoned-up" on the intake manifold, try shining a small flashlight into the throat of the carb to see if you have any light leaks. Do this in a darkened room, for better results.

    Also be sure to check other areas, like the top throttle plate. Keep us posted.

    Old Skool
  16. Dyran

    Dyran New Member

    i made a gasket for what i thought was wrong, but i still cant ride it with out choking it... im going to take apart my carb again and look at it further, i'm not sure where any other leaks could be
  17. motorpsycho

    motorpsycho Active Member

    Again, normal hardware store o-rings will swell when introduced to fuel. If it swells, it car come apart and end up getting sucked into the engine.
    You will need to get o-rings that can withstand contact with gasoline.
    It still sounds like there's an air leak somewhere.
    Shining a flashlight into the carb and looking for "light leaks" won't give you much success in my opinion. The best way to find an air leak is to get the engine running, let it idle and spray starting fluid (in very small bursts) around the carb and intake manifold.
    Concentrate on one area at a time and listen for the engine to rev up on its own.
    If you shoot starting fluid at the intake to carb seal area, (for example) and the engine races up on it's own, you just found your leak. The air leak will suck the starting fluid into the engine and it will find the tinyest of leaks that you would never even be able to see.

    Are you sure that you are actually choking the engine? You may have the choke on when you think that you have it off.
    The choke on a cns carb works backwards from how a normal choke works. You open the choke for cold starting, and close the choke once it warms up. The "choke" is nothing more than a brass rod that slides up and down in it's own hole next to the throttle slide in the carb. The brass rod should be fully closed (down) for "choke off" (warm engine) and fully open (up) for "choke on" (cold engine).
    When the choke is "on" (brass rod up) it delivers more fuel to the carb to richen the air-fuel mix for easier cold starting, rather than restricting the air flow to richen the mixture like a normal butterfly style choke.
    my 73 Kawasaki 2 stroke 100 enduro has this exact style of choke set up on it, so i know how this style of choke works.
    Last edited: Jul 11, 2011
  18. Old Skool

    Old Skool New Member


    You are correct and I have no argument with the starting fluid test - except it has some potentially dangerous side effects - being such a fire hazard. As an old dude who has been around the block a time or two, I tend to stay away from using starting fluid on an engine that is currently running. I am not being critical of your method, but I am somewhat more safety conscious. Too many things can go wrong ... and they happen very quickly.

    The flashlight in the carburetor throat is a much safer method and I have used it on other occassions to find potential problem areas. If someone burned themselves badly, based upon one of my recommendations, I suspect that I would carry that guilt for a long time.

    As previously atated - I had the same problems that Dyran is having and went through some of the same processes. It was obvious that my carb was running too lean also, because the choke had to be used on mine to get the engine to respond. An O ring was not my problem and probably is not the problem in his situation either. I am still using the original O ring.

    My air leak came from the top throttle plate, and I fixed that with a small gasket. The other "still too lean" issue was remedied by moving the gas needle position from position # 2 to #3.

    Then - a cable adjustment and a little additional tweaking of the exterior adjustment screws put me in business.

    And also as I previously mentioned - the physical act of "showing" someone something is much more valuable than many words of text. Dyran will eventually find his problem and will be much richer in the experience. Along the way, I would not wish to be responsible for accidents or injuries that he could potentially suffer.

    Old Skool
  19. Old Skool

    Old Skool New Member

    By the way ... I forgot to mention that I grew up in an oil field town and continue to reside in the "oil patch - so when we purchase such things as gaskets and O rings around here - they are usually darn near bullet proof.

    I do understand that not everyone has access to some of the better quality stuff, but I doubt that any O ring that was purchased in a supply store in this area would ever get soft in anything as puny as a little gasoline. --grin--

    Blessings to ya' buddy.

    Old Skool
    Last edited: Jul 11, 2011
  20. motorpsycho

    motorpsycho Active Member

    this is one of those cases where "you're right about everything and i'm just another moron."
    sorry dude but i know what i'm talking about, and i know that the potential for a fire with starting fluid getting sprayed around an intake manifold is little to none.
    unless you are a total idiot and totally soak the motor with the stuff, there can't be a fire.
    the starting fluid will get sucked into ANY tiny air leak and get burned INSIDE the combustion chamber.(this is why i said use a tiny amount in short bursts and concentrate on one are at a time).
    how in the he-- can you find an air leak with a flashlight?
    if you have a double over lapping flange and the air leak is around a corner, how in the heck can the light find it's way out?
    a flashlight can't turn corners.
    90% of the typical hardware store o-rings are made for plumbing (water) and are just rubber.
    I'm telling you that they will not hold up to to gasoline.
    do some research and you'll find that out for yourself.
    I don't give 2 craps if you grew up in an oil field town or on an oil rig.
    That doesn't mean jack to me and how can that make you the king of o-ring knowledge?
    i've been building engines since i was 12 years old, i've built drag cars, street cars and motorcycles. My dad has been a mechanic for over 50 years and he has owned his own shop for over 30 years. i learned everything i know by growing up watching him, and working for him. I've been working on , restoring, rebuilding all things mechanical for well over 30 years and there really isn't anything out there that i can't fix or diagnose. anyone can replace parts but not everyone can diagnose a problem without being wrong.

    all it takes to use starting fluid is a little common sense.
    you wouldn't go and dump a 5 gallon can of gas onto a fire would you? no...because that would be dumb and your common sense would tell you not to do it.
    same thing applies with starting fluid. don't go overboard and don't soak down the whole engine, and it'll work just fine with no danger.
    Last edited: Jul 12, 2011