Ideas how to contain carb spit-back

Discussion in 'Motorized Bicycle General Discussion' started by Alajoyn, May 9, 2010.

  1. Alajoyn

    Alajoyn New Member

    Joined:
    Sep 28, 2009
    Messages:
    71
    Likes Received:
    0
    Anyone have advise on an appropriate air filter system that will better contain the fuel spit-back that is inherent in the HT engine design? I have fuel that accumulates at the bottom of my stock air filter system on the stock NT carb. I realize that with a single cylinder single carb set up on a 2-stroke you'll have this issue, but those of you with custom paint, what do you do to prevent dripping and getting onto the motor and it's fins...except a wipe rag every 5mi or so.

    Ideas?

    Thanks,
    Robert
     
  2. bairdco

    bairdco a guy who makes cool bikes

    Joined:
    Aug 18, 2009
    Messages:
    6,350
    Likes Received:
    25
    i wipe mine with a rag every 5 miles or so.

    actually, i don't think there's a cure for it. if you got a bigger filter to soak it up, it'd just get saturated and have to be cleaned out more often to provide good airflow.

    the right mixture helps a lot. i use 100:1 opti 2 oil, and the oil doesn't clog up in the filter and leak out as much.
     
  3. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,301
    Likes Received:
    26
    I concur with Bairdco. It's a 2 stroke and intake blow-back is normal. Either live with it or keep a rag handy, or go for a 4 stroke engine.
    Some of the more exotic, synthetic oils. Opti-2 is an example will reduce the amount of oil in the intake by some degree but you'll always have it. Sorry, just a fact of life.
    Tom
     
  4. corgi1

    corgi1 New Member

    Joined:
    Aug 13, 2009
    Messages:
    2,282
    Likes Received:
    1
    Would a plastic overflow tube from the bottom of the air-filter housing going down below the frame help ? (as seen on 4 stroke carbsw on a thread here )
     
  5. Goat Herder

    Goat Herder Gutter Rider

    Joined:
    Apr 28, 2008
    Messages:
    6,251
    Likes Received:
    2
    On one of my builds I had played with a boost bottle, and put of all things a Right Guard deodorant cap. It matched the color of the bike almost. Last I used pantie hose about 6 plies with a cable tie around the end. It really wasn't all that pretty but the oil was contained between the boost bottle and the added depth of the cap I used.

    I think a bigger deeper filter might help but have not tried it without the boost bottle.
    And no the boost bottle doesn't give any dramatic power just makes the throttle a little more responsive.
     
  6. Nougat

    Nougat New Member

    Joined:
    Nov 4, 2009
    Messages:
    1,332
    Likes Received:
    0
    To really fix it, you'd need to add a reed valve.
     
  7. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    2
    Just don't route it to oil your tire.
     
  8. Alajoyn

    Alajoyn New Member

    Joined:
    Sep 28, 2009
    Messages:
    71
    Likes Received:
    0
    Oh yeah, I like the idea of fitting tube to bottom of air filter housing.
    I could fabricate a housing that fits tightly around and seals at the carbs front face and make the new housing with a little "basin" with a ferrule fitting soldered to attach a tube to. I can fab it from copper shimming stock and solder it together with an internal flange to press the filter against, then cap it mebe even with the same cover & longer screws. Hmmmm new things to invent.
    Thanks for the idea guys.

    Robert

    Hmmm or would enlongating the intake manifold with a slight "s" help eliminate it??
    More to make ya go hmmmm
     
  9. CoastalCruiser

    CoastalCruiser New Member

    Joined:
    Apr 28, 2010
    Messages:
    338
    Likes Received:
    0
    ya beat me to it Corgi. That's what I'd do.
     
  10. Drewd

    Drewd New Member

    Joined:
    Jul 25, 2008
    Messages:
    425
    Likes Received:
    0
    Believe it or not, this is the only instance I'd recommend a boost bottle for a HT. Mine had less spitback with one but no improvement in top end performance or speed.
     
  11. Cabinfever1977

    Cabinfever1977 New Member

    Joined:
    Mar 23, 2009
    Messages:
    2,290
    Likes Received:
    1
    Or you could connect a hose or rubber boot on the end of the aircleaner and run it to a airbox,it contains the oil and gas and holds it in the aircleaner housing. i know this works cause i tryed it.
     
  12. corgi1

    corgi1 New Member

    Joined:
    Aug 13, 2009
    Messages:
    2,282
    Likes Received:
    1
    Thinking about the boost bottle,it is a vaccume thing,,,,,so if the tube from the bottom of the air filter was placed in front of the carb intake the vac.from the engine running would suc the oil mix that was collecting in the tube from the bottom of the air filter keeping it clean
     
  13. Cabinfever1977

    Cabinfever1977 New Member

    Joined:
    Mar 23, 2009
    Messages:
    2,290
    Likes Received:
    1
    You would also have to have the aircleaner filter sealed tight up against the housing or gas/oil will leak from the cracks. You also have to have it removable to clean it.
     
  14. Fabian

    Fabian New Member

    Joined:
    Sep 9, 2009
    Messages:
    168
    Likes Received:
    0
    There's only one solution to eliminating intake reversion, and that's to fit a reed valve onto the intake port.
    This method will not only solve reversion issues but will increase low and mid range rpm performance.

    Now if only someone can design and market a reed valve intake conversion system, i'll buy the damm thing at an instant.

    Fabian
     
  15. Alajoyn

    Alajoyn New Member

    Joined:
    Sep 28, 2009
    Messages:
    71
    Likes Received:
    0
    Yeah I know what your talking about.
    I have a buddy that designed his own external reed mod for an old Mercury 3cyl outboard in order to increase performance over the stock reed system. I've seen it. Wow it made a difference, Kinda like runnin the old Cleveland 351 heads I used to play with.
    Well, a grinder, an aluminum block and lots of epoxy'll get ya there...eventually.

    Robert
     
  16. jawbreaker

    jawbreaker New Member

    Joined:
    Jun 30, 2010
    Messages:
    10
    Likes Received:
    0
    how is a reed valve work?
     
  17. NunyaBidness

    NunyaBidness Active Member

    Joined:
    Jun 29, 2008
    Messages:
    1,062
    Likes Received:
    1
    A reed valve fits in the intake between the carb and the cylinder. This allows fuel to get sucked into the cylinder yet closes to prevent any fuel from going back towards the carb. Basically a reed valve is a one way valve.
     
  18. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

    Joined:
    Mar 20, 2008
    Messages:
    6,170
    Likes Received:
    18
    K&N style filters tend to soak up the oil. (^)
     
  19. ferball

    ferball New Member

    Joined:
    Apr 8, 2010
    Messages:
    599
    Likes Received:
    0
    The reed valve sounds interesting, is there any temperature issues to worry about when attaching stuff to the intake? Just curious as this may need some exploration on a rainy saturday afternoon.
     
  20. 5446

    5446 New Member

    Joined:
    Jun 7, 2010
    Messages:
    84
    Likes Received:
    0
    Ya and I would be right behind you!
     

Share This Page