Too much fuel, not enough air.

Discussion in 'Motorized Bicycle General Discussion' started by Targan, Aug 30, 2013.

  1. Targan

    Targan New Member

    Joined:
    Jun 22, 2013
    Messages:
    56
    Likes Received:
    0
    I have a grubee slant head 66cc engine with an NT carb, and an expansion chamber with that silver silencer thing on the end. Basically my bike boggs and has almost no power, it is VERY jerky and will not reach top speed. This all happened out of no where too. I cleaned my carb and adjusted my needle to the leanest possible setting. I also cleaned my filter and tried running with it off as well. My plug still comes out black, oily, and wet. It seems like not enough air is reaching the engine. I tried running with the expansion chamber completely off for a couple of minutes and no difference (except now I'm deaf lol). My spark plug sparks just fine. I am out of ideas.:-||
     
  2. bairdco

    bairdco a guy who makes cool bikes

    Joined:
    Aug 18, 2009
    Messages:
    6,334
    Likes Received:
    19
    what's your fuel mixture? with regular crappy oil it should be 24:1 for break in, and 36:1 afterca few tanks.

    running without a pipe will heat the motor up like crazy, so thats not a good idea.
     
  3. Targan

    Targan New Member

    Joined:
    Jun 22, 2013
    Messages:
    56
    Likes Received:
    0
    The engine has about 300-400 miles on it already. I was running 32:1 when the bogging started. I thought it was a too much oil issue at first so I drained it then added a 40:1 mix. Nothing changed. I have done all the textbook inspections. Everything is clean, I get fuel (too much), spark, and air (not enough it seems). I moved the needle clip in the carb to the leanest setting (nothing changed), then to the richest setting (bike wouldn't even start), then back to the leanest. The bike origanally ran on the middle clip setting just fine for a week or 2 when I installed the NT carb. Any use of choke and the bike dies which tells me it's an air issue.

    *Side note*
    This same issue happened on my old CNS carb (never found out why. The CNS carb ran fine for 3 months straight). I changed it out for this new NT carb, it ran well for 2 weeks, then BLAM, bogging badly again.
     
  4. Huffydavidson

    Huffydavidson STREETRACER/MANUFACTURER

    Joined:
    Jan 29, 2012
    Messages:
    1,075
    Likes Received:
    0
    It sounds like you moved the clip the wrong way. When moving the clip UPWARD the needle drops down leaning your fuel . Another thing , once your plug has gone black it won't come back to a lighter color. You'll have get a fresh plug . If you have leaned it to the TOP natch and plug is still running black then its time for you to JET DOWN . I mit be wrong but , as I recall most It's come with a .70 jet. So you'll be needing a .68 jet IF I'M CORRECT ABOUT THE STOCK JET SIZE. SICKBIKEPARTS sell single NT jet reasonably priced and then a response on shipping well let's just say the rocketshipper's.
     
  5. fatdaddy

    fatdaddy New Member

    Joined:
    May 4, 2011
    Messages:
    1,516
    Likes Received:
    0
    I would also suggest checking the float needle to make sure it's working and not causing an overflow problem. THis could also dump too much fuel into the cylinder.
    fatdaddy.
     
  6. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,301
    Likes Received:
    25
    If the bike was running good then started with this "bogging" thing I doubt you're looking at a jet size problem. Something else is responsible. You say the same thing happened with the CNS carburetor and now the NT. They both ran good then started acting up.
    If it was jet size the problem wouldn't just appear after a few miles.

    I concur with fatdaddy in that you might have a float or float valve problem that is allowing too much fuel in the bowl. Are you using an in-line fuel filter? Possibly the float valve is not closing due to trash in the seat.
    Are you using fresh gasoline? 2 cycle mix has a short 'shelf life' and should only be stored for a few weeks. Old mix won't perform as well as a fresh batch.

    What plug gap are you running. .024 to .028 is a good ball park place to start.

    Also keep in mind that the needle clip position only effects fuel flow at or below 3/4 throttle. Above that, up to WOT the main jet determines fuel/air mix.

    Tom
     
  7. Targan

    Targan New Member

    Joined:
    Jun 22, 2013
    Messages:
    56
    Likes Received:
    0
    Great response, thank you. I have checked the carb and cleaned it out, as well as using fresh gas. Spark plug gap is .026. I am using an inline fuel filter too. I called a guy who repairs these bikes and said something about it being piston rings? I'm good with the basics but I'm not very knowledgable about the actual engine. He said the piston rings probably need replacement. Literally everything on my bike is 100% good to go, working, and clean, EXCEPT the engine. I have not looked into that because I don't know what to do or how to work on them. The engine is VERY oily inside and out. I repeat: I am using a 40:1 ratio.
     
  8. Targan

    Targan New Member

    Joined:
    Jun 22, 2013
    Messages:
    56
    Likes Received:
    0
    I forgot to mention that starving the bike of fuel did not seem to help either. I tried running with the petcock off, stayed jerky until it died. Tried draining the float, stayed jerky until it died. It helped somewhat, but not enough to label the float as the problem.
     
  9. CTripps

    CTripps Active Member

    Joined:
    Aug 22, 2011
    Messages:
    1,311
    Likes Received:
    0
    Not sure if it'll have an effect, but have you checked for gunk/blockage of your exhaust?
     
  10. Targan

    Targan New Member

    Joined:
    Jun 22, 2013
    Messages:
    56
    Likes Received:
    0
    Yes, I even tried running my bike without the exhaust on. No change
     
  11. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,301
    Likes Received:
    25
    This might sound silly, and it wouldn't apply to the CNS carb but have you checked to make sure the choke plate is fully open and isn't vibrating closed?

    Tom
     
  12. fatdaddy

    fatdaddy New Member

    Joined:
    May 4, 2011
    Messages:
    1,516
    Likes Received:
    0
     
  13. Targan

    Targan New Member

    Joined:
    Jun 22, 2013
    Messages:
    56
    Likes Received:
    0
    Unfortunately it's solid as a rock. Open as can be. Any replies about the piston rings being the issue? I still have no idea what they do or where they are. Guy i called said they were probably the issue, but i want to fix it myself since I'm broke.
     
  14. bairdco

    bairdco a guy who makes cool bikes

    Joined:
    Aug 18, 2009
    Messages:
    6,334
    Likes Received:
    19
    its possible you cracked a ring, but normally that will destroy your piston, jug, and possibly everything else.

    in short, theres two rings set into grooves around the piston. they expand to form a seal which gives you compression.

    if you blew a ring, normally the parts fly around inside and gouge up the cylinder walls, crack your ports, chew up bearings, and all sorts of other nasty stuff.

    and it's pretty obvious. it wouldn't just run rich. unless you got really lucky and the chunks blew out your exhaust before causing damage.

    you can pull the head off and look for grooves in the cylinder walls.

    on old cars the rings wear down eventually causing low compression, oil loss, etc, but our engines don't normally last long enough for that to happen. it's usually a catastrophic breakdown.
     
  15. fatdaddy

    fatdaddy New Member

    Joined:
    May 4, 2011
    Messages:
    1,516
    Likes Received:
    0
    I think the rings would have to be REAL bad to not let the engine at least POP a little. Perhaps GONE and laying in the lower case. Otherwise it should at least ACT like it wants to start and go pop pop once in a while. I guess yer gonna hafta pull the cylinder and check. or just do a compression test.
    fatdaddy.
     
  16. Huffydavidson

    Huffydavidson STREETRACER/MANUFACTURER

    Joined:
    Jan 29, 2012
    Messages:
    1,075
    Likes Received:
    0
    A lot of auto part stores have a loan-a-tool program, were you put down a deposit use the tool, return it and get your deposit back on the spot. That's what I did @ Auto Zone .
     
  17. Targan

    Targan New Member

    Joined:
    Jun 22, 2013
    Messages:
    56
    Likes Received:
    0
    Hey guys, so both my piston rings were broken. They stayed inside of the grooves "lucky me. I ordered new ones. I never installed these before, is there a special process or trick to do?
     
  18. crassius

    crassius Well-Known Member

    Joined:
    Sep 30, 2012
    Messages:
    3,475
    Likes Received:
    44
    first, grow your thumbnails a bit long for spreading the new rings over the piston (there is a tool for this if you're going to do it a lot)
     
  19. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,301
    Likes Received:
    25
    When it comes time to install the new rings you'll need to be very careful and not break them. They aren't made of rubber and will only stretch so far to go over the piston. Go slow and carefully work them on in a circular motion into the ring grooves.

    There are ring gap alignment pins in the piston ring grooves. The gaps of the rings must align with those pins or the rings can not be compressed enough to slide back into the cylinder bore. Lubricate everything, rings, piston and cylinder with whatever oil you use in your fuel mix before reassembly.

    My concern is that if you had broken rings that there is damage to the cylinder walls. It would be rare that the rings would break when the engine is running and there not be damage to the cylinder. Inspect the cylinder walls for gouges. A damaged cylinder will not allow the new rings to seal and you'll be back to square one and will have wasted you money and time buying new piston rings.

    Tom
     
  20. crassius

    crassius Well-Known Member

    Joined:
    Sep 30, 2012
    Messages:
    3,475
    Likes Received:
    44
    Oh, just remembered - last time I saw a set of broken rings, I pushed a small magnet on a piece of flexible plastic around the bottom of the case - found some tiny pieces of ring
     

Share This Page