Carby Carb Issue---leaking fuel and running poorly

Discussion in '2-Stroke Engines' started by Chimpo, Sep 26, 2010.

  1. Chimpo

    Chimpo New Member

    I just got my new MB up and running. Its a Grubee Skyhawk 66/80 from gas bikes. I have less than 10 miles on it. I am still running 16:1.

    The AWESOME instructions leave out any mention of the hoses running off the carb. I have two of them that run to no where. The one that concerns me most is pictured below.

    The hose is on the starboard side of the motor. It runs from the bottom of the bowl to nowhere. What really bothers me is that it steadily drips gas down my leg as I ride.

    I took the bike for about a 20 minute ride today. For the first 15 minutes it ran fine, for a Chinese 2 stroke. The last few minutes it began to bog down. I fiddled with the choke and got it to run better.

    At the very end the bike would start but not increase in RPM. It would bog out when I gave it gas. I had to give it gas AND pedal (while its running) to get the motor running right.

    Fortunately I was close to home.:sweatdrop:

    The spark plug looks a bit wet.

    I assume that the fuel leaking from that hose is not how the China Men intended it to be.

    Attached Files:

    Last edited: Sep 26, 2010

  2. motorpsycho

    motorpsycho Active Member

    that hose may be a drain hose for when you want to drain the float bowl...but normally the drain is just a screw with no hose on it. if it was a drain hose, there would be some kind of screw or valve on the carb to allow you to open and close it. I don't think it's a vent tube, because normally vent tubes are on top of the float bowl...this one is on the bottom of the float bowl.
    i'm not sure about the other tubes, but they look like vent tubes really.
    the other thing that MAY be happening is that your float level may be set too low, which is allowing the carb to flood over. if the float is set too low, the bowl will fill up with fuel before the needle & seat have a chance to close and this would cause the carb to flood over.
    the only thing these carbs need is a main fuel feed and a vent (or more than one vent) to equalize the pressure in the float bowl.
    you should really consider running an in-line fuel filter because a TINY peice of dirt will clog up your main jet. sometimes the tanks that come with these kits have a lot of debris in them when you take them out of the box. even tho the petcock has a screen filter on it, they aren't the best.
    Last edited: Sep 26, 2010
  3. HeadSmess

    HeadSmess Well-Known Member

    occasionally the drain screw thingy has , inside the bowl, a small tube running up that communicates directly with the drain hose. depends on carb brand model series version etc... :p

    the overflow. taking off the bowl and having a look helps.

    so it sounds like your float level is too high. or the needle isnt closing due to gunk...stiffness...

    now this is handy way of checking. keep the bowl on, hose attached, hold hose against the carb. open the drain screw at the bottom a turn or two.

    hose fills up and shows the TRUE level inside the bowl... you want it about 3-4mm below the top of the bowl.
    sort of hard to see any other way...strange that.

    any higher, you need to remove bowl, and carefully bend the tangs on the float up slightly... then recheck level, etc ...

    get used to taking off that bowl a lot if you really want to tune the carb to its true potential...

    cant wait for my new mikuni vm18 to arrive :D
    Last edited: Sep 27, 2010
  4. Chimpo

    Chimpo New Member

    I turned on the fuel valve to try that nifty hose/fuel level trick. When the fuel valve was turned on, gas started pouring out of the air filter. I'm no mechanic but I took this as a clue that the fuel level was set too high. The hose trick showed the level about 3/4'' above the bowl rim.

    I took off the bowl and found black residue at the bottom of it. I cleaned it out. I adjusted the needle height and reassembled.

    I'm going to wait until later tonight, when I can go get a fuel filter, before I test it. I'll let you all know.
  5. HeadSmess

    HeadSmess Well-Known Member

    mmmm, black residue....

    always pay to clean even new carbs ;)
  6. Chimpo

    Chimpo New Member

    I assumed the residue came from the fuel line or tank. Who knows?

    I think the problem is solved. I ran the bike for a few miles last night and all was well. It still needs some tweaking to smooth things out, but I don't think it going to leave me stranded now.

    Thanks for the advice!
  7. trydrew

    trydrew New Member

    I had an overflow problem recently on my GT5 carb (<20mi) that seemed to come about shortly after I took the bike over a curb. I wasn't far from home (<1mi), but my first thought was that the float got hung up. I tried tapping on the bowl, but it just kept spilling over. I sputtered home, doing more peddling than normal, and then continued to drain remove the bowl.

    Upon initial inspection, float wasn't stuck (I was careful not to bump it with the bowl). That was a bit perplexing, until I tried to push the float up (carb right side up). It didn't move! The fuel shutoff pin had dislodged from the housing and wedged itself at an angle that held it in place incorrectly. There was a retention clip to hold it to the float flange. I simply modified its fitment to prevent this from happening again.

    I hope this will be of help to someone.