CNS carb- fuel overflow/drainage line not working!?

Discussion in '2-Stroke Engines' started by Fletch, Mar 18, 2011.

  1. Fletch

    Fletch Member

    I think there is a hole in my float or something because I checked the float level and it was good, but the carb is still flooding all the way up into the 90 degree rubber part of my air filter and 'gargling' in there!!

    Meanwhile not a single drop of fuel out of the drainage line at the base of the bowl! I had the carb apart and blew in the the drainage piece to make sure it wasn't clogged up and it wasn't. How can air get through but fuel won't?

    I don't understand what's going on? The only guess I have is that the overflow piece that is inside the bowl which sticks up is too high, and the fuel is going up the pilot or main jet and then overflowing into the air filter and engine. Although some fuel would be bound to end up in the drainage?

    I need some serious ideas on this one guys ;:confused:

    Come to think of it, I never had any fuel come out of the drainage line when I had a CNS before on another bike. The only time I ever saw fuel come out of that line was when I had the tube attached from it around to the air vent on the top of the carb which created a vacuum effect. It was never strong enough to pull the fuel all the way through the tubing to the top and in, but the fuel would come out into the tubing and then go back... like it was being used "as needed" . But that other CNS never flooded up like this.

  2. Dave C

    Dave C Member

    There appears to be a lot of difference between V1 and V2 of the CNS carb. With the V2 being a piece of junk.

    I don't have one so I have no clue on a fix. I've converted street carbs to raceing in classes that limited the racers to stock carbs. All I can say is after not doing it for 10 years I still get calls to do what I do...told them I would. :p I got three to rebuild for now....the guys tell me they can get me more biz but I'm not sure if I want to, can't make enough for the time put into it :\

    I'm thinking about getting one of the newer CNS carbs to experiment on but $50 for a toy to play with....
  3. goodtime65

    goodtime65 Member

    I had this problem and I relay had to lean the float out and the bike ran a lot better
  4. Fletch

    Fletch Member

    I've been thinking about it and I think you're right. I measured the fuel in the bowl though and it was below the edge of the bowl by a decent amount. The strange thing is this happened twice after riding and both times there was no overflow or leaking of fuel prior to riding. I was thinking maybe the float needle is getting stuck down, but I don't see how that can happen really. I am going to lower the float by a large amount and see if it keeps up. I realize now that the fuel is coming up through the air hole at the bottom of the air filter side of the carb. There's an airway there that goes down into the bowl via a small hole. I dunno what else it could be other than the float, but I don't understand why it was not leaking until I started riding. I had the bike idling before I took off. Then after riding whenever I would stop and idle, the engine would get flooded and take a while to start up again after peddling a ways. I didn't see a leek because the air filer was trapping all the overflow and then I heard this gargling sound that freaked me out until I realized what it was. I have a 90 degree air filter that was acting like a cup for all the excess fuel.
  5. goodtime65

    goodtime65 Member

    the small vent that you talk about is an overflow for the bowl. If fuel is comming out this than the float level is definitly to high
  6. Fletch

    Fletch Member

    Yeah I know it is... I'm saying fuel isn't coming out, yet it isn't clogged up and I'm not sure why. The fuel is filling all the way up into the venturi and then into the rubber air filter manifold which acts like a big cup. Then it gargles as it slowly drains into the engine and floods it. Considering I can't get the overflow valve vent to work, I'm just going to have to lower the float more, even though I measured it and it was well below level with the bowl, so I'm stumped as to why it's even overflowing. I was thinking maybe the fuel stop needle is getting stuck in the open position somehow because it's only after riding this happens.
  7. motorpsycho

    motorpsycho Active Member

    check for dirt in your needle & seat. even tho your float is going all the way up, the needle may not be closing all the way, causing fuel to overflow through the main jet into the carb.
    But that still doesn't explain why there is no fuel coming out of the overflow vent. Fuel should come out of the overflow before it gets high enough to flood into the carb through the jet.
    this is a strange one.
  8. Fletch

    Fletch Member

    I know it's weird... I was wondering... could it somehow be coming from the secondary fuel passage (ie. the choke on the cns)? Maybe the "stopper" that is attached to the cable that you control with the shifter on the handle bars isn't seating all the way and fuel is coming out through there? I'm not sure really how that whole passageway routes and works, only that the choke doesn't choke air, but adds fuel when you lift that stopper up.

    What happens when riding though that doesn't happen when idling or before that is causing something to change inside? Vibration? with the bowl off I turned opened the fuel line and let it flow out so that I could push the float up and make sure it is stopping the fuel... and it is. So I don't think it's dirt in the needle. If it's going to overflow it should do it with the engine off just sitting with the fuel line open and it hasn't done that. I've left it open and let it sit long enough to where it would have definitely overflown. Something is changing after I ride for a bit and I am stumped as to what it could be.

    The only thing worth mentioning is that I bought this carb used on ebay and I got it in weird condition. The needle jet was lower than the other CNS I have. So the round part that sticks up into the venturi that the needle goes into was flush with the bottom of the venturi as opposed to raised up a few millimeters like you usually see on carbs. I tried pushing it up with no luck. I culdn't get the **** thing out either so I drilled it out. I took a needle jet from my broken CNS and put it in, but it topped out at the same place, so I drilled the opening larger until I could push it all the way up to where it should be. I'm wondering if fuel is leaking up around the needle jet from drilling it now. It's fit in there really tight and I had to jam it in, so I'm questioning this theory, but I've got nothing else. I have another bowl from the other cns... should I swap bowls and see if that overflow jet works?