2011 CNS V2 Carb Bogging

Discussion in '2 Stroke Bicycle Engines & Kits' started by mxchris727, May 24, 2011.

  1. mxchris727

    mxchris727 New Member

    Joined:
    Aug 10, 2009
    Messages:
    34
    Likes Received:
    0
    Hi all,
    I have recently purchased a Grubee Skyhawk GT-5 form gasbik.net. The build was quick and perfect and the engine fires up on it's first stoke. The problem that I've been having is that when I open the throttle anywhere past the 1/4 position, it boggs down until it idles. When idling, the engine seems strong and pulls hard (I can go about 12mph with lots of power) but anywhere beyond, it cuts out. Also, I can run it up to full speed if I keep the choke half-way on (acts like it has an air leak).

    So far, I have tried all of the needle positions, bent the float so that more fuel is stored in the carb without overflowing (and tried the other way), cleaned the main jet, and used silicone gasket sealant around the intake where the carburetor connects. I have preformed a intake air leak test with WD40, carb cleaner, and water but found no air leaks at all. Also the spark plug is wet from the break-in mixture.

    Any ideas? Here are some specs:
    Miles on engine: 8.5
    Oil/Fuel ratio: 18:1 non-synthetic (has worked fine for my past 2 engines)
    Spark plug condition: Wet with the three prongs gaped correctly.
    Jet needle: 2nd notch from top
    Fuel: 89 octane
    Nothing connected to the white wire (everything is isolated)

    Thanks,
    Chris
     
  2. DuctTapedGoat

    DuctTapedGoat Active Member

    Joined:
    Dec 20, 2010
    Messages:
    1,179
    Likes Received:
    9
    I think it's an inherent problem with the choke on CNSv2 tbh.
     
  3. flatblack

    flatblack New Member

    Joined:
    May 22, 2011
    Messages:
    374
    Likes Received:
    0
    Running too lean on the top end?
     
  4. mxchris727

    mxchris727 New Member

    Joined:
    Aug 10, 2009
    Messages:
    34
    Likes Received:
    0
    Yeah, the plug looks white if I run it for brief periods of time at top-end.

    I just bought a NT carb from boygofast, when it comes I'll see if there is any improvement.
     
  5. flatblack

    flatblack New Member

    Joined:
    May 22, 2011
    Messages:
    374
    Likes Received:
    0
    Thought so. Just need to figure out the culprit. Rejetting could help. I'm not totally familiar yet with these carbs/motors, but my experience with nitro R/C and 250cc Quads told me that could be the problem. It's a new learning curve. But some of the basics still hold true.
     
  6. Tad Bit Tipsy

    Tad Bit Tipsy New Member

    Joined:
    Jan 2, 2010
    Messages:
    478
    Likes Received:
    0
    Go Synthetic, reduce ratio to 32:1 or even 40:1, that's what the CNS likes to eat, lol, no seriously, think about it, it's a performance carb!
     
  7. Greg58

    Greg58 Well-Known Member

    Joined:
    May 1, 2011
    Messages:
    3,903
    Likes Received:
    763
    Search at carb and intake.
     
  8. mxchris727

    mxchris727 New Member

    Joined:
    Aug 10, 2009
    Messages:
    34
    Likes Received:
    0
    With only 15 miles on the engine, I don't think I should lean the ratio or switch to synthetic yet.
    I have used gasket sealant to the intake but that did not help at all. I think I will need to rejet...
    Do you think the NT carb will preform as well as the CNS if it was working correctly?
     
  9. Greg58

    Greg58 Well-Known Member

    Joined:
    May 1, 2011
    Messages:
    3,903
    Likes Received:
    763
    Try removing the small hose that vents the bowl.
     
  10. biknut

    biknut Well-Known Member

    Joined:
    Sep 28, 2010
    Messages:
    6,503
    Likes Received:
    194
    I got the exact same problem, but I can only do maybe 10 mph.
     
  11. DuctTapedGoat

    DuctTapedGoat Active Member

    Joined:
    Dec 20, 2010
    Messages:
    1,179
    Likes Received:
    9
    The NT carb technically doesn't perform as well as the CNSv2 when working correctly. But - there is an insanely high percentage of people who never get their CNSv2 carb working at all.
     
  12. biknut

    biknut Well-Known Member

    Joined:
    Sep 28, 2010
    Messages:
    6,503
    Likes Received:
    194
    What did you do to get yours working?
     
  13. DuctTapedGoat

    DuctTapedGoat Active Member

    Joined:
    Dec 20, 2010
    Messages:
    1,179
    Likes Received:
    9
    Wasn't mine - was a friend's bike he wanted to motor. I told him to get a simple 48cc Raw kit, and he ended up getting a 66cc gt5 and paid extra for the CNSv2 carb.

    Only time I've ever seen one, and it's just the inherent problem. I've seen lots of fixes posted that people do to get them working - removing certain tubes, removing all tubes, fixing intake seal, jet wasn't secured at all and was sitting on the bottom of the float bowl, etc etc.

    When I was running it though, it felt to me as though it was a choke issue, like you couldn't actually turn the choke completely off.

    I need to get one and find a way to fix it, but they're too expensive. I'd like to try and gut the choke completely out of the unit - as in the CNS carbs the choke is cabled etc. I can't say it'll work if anyone else tries, but I know I myself want to remove the entire choke assembly and see if that'd be a valid fix.

    I only know they can work well from people online who have it work well out of the box and they claim it works great.
     
  14. biknut

    biknut Well-Known Member

    Joined:
    Sep 28, 2010
    Messages:
    6,503
    Likes Received:
    194
    That's cool. I understand where you're coming from.

    I've been working all day on jetting a new SkyHawk 80 with a CNS v2 carb. Out of the box this motor ran so bad that it would basicly just start and idle. Giving it any gas at all resulted in it boging and stalling out completely unless you let off the gas. Then it would at least idle.

    Now it's running in a much more normal manner. What I had to do was drill the F out of the main jet. The size that's working best for me is equal to a #67 drill bit. Stock was equal to about a #71 drill bit. A 71 size is smaller than a 67. I also raised the float level 3 times, but I didn't notice too much from that. I can't say it hurt anything either. Mostly the issue seems to be the main jet being about 4 sizes too small out of the box..

    I tried with and without the rubber float bowl vent tube, and I couldn't tell any difference.
     
    #14 biknut, May 28, 2011
    Last edited: May 28, 2011
  15. Greg58

    Greg58 Well-Known Member

    Joined:
    May 1, 2011
    Messages:
    3,903
    Likes Received:
    763
    What I have learned about these little engines is that they are picky, what works on mine may not work on others. Mine is a 48cc grubee angle head, e-clip on 3rd notch, sbp air cleaner oiled with k/n oil, vent tube removed from air filter base, copper sleeve to replace the plastic spacer. weed blower filter on vent.
     

    Attached Files:

  16. mxchris727

    mxchris727 New Member

    Joined:
    Aug 10, 2009
    Messages:
    34
    Likes Received:
    0
    I'm going to try drilling out my jet; Is it as simple as taking a drill and widening the hole? Ill let you know how it goes...
     
  17. biknut

    biknut Well-Known Member

    Joined:
    Sep 28, 2010
    Messages:
    6,503
    Likes Received:
    194
    You wont need a drill. I just turned the bit with my fingers.
     
  18. mxchris727

    mxchris727 New Member

    Joined:
    Aug 10, 2009
    Messages:
    34
    Likes Received:
    0
    All of the hardware stores in my area don't carry the #67 sized bit. BUT... I think I solved the problem!
    I removed the black tube that connects the vent to the intake and it's running much better now! I think the connection was creating a vacuum that was not letting the gas flow up the main jet correctly. Still running very lean though-
     
  19. biknut

    biknut Well-Known Member

    Joined:
    Sep 28, 2010
    Messages:
    6,503
    Likes Received:
    194
    I couldn't tell any difference when I did that.
     
  20. Greg58

    Greg58 Well-Known Member

    Joined:
    May 1, 2011
    Messages:
    3,903
    Likes Received:
    763
    If you can find a torch tip cleaning set you can open up the jet, there are 12 or so very small round files in a folding set. Be careful a slight change in size can make a big differance.
     

Share This Page