Carby Lean condition? General tuning questions before purchase

Discussion in '2-Stroke Engines' started by Khronokai, Aug 3, 2009.

  1. Khronokai

    Khronokai New Member

    I'm considering a purchase. The bike is an OCC stingray. BGF 66CC engine, 44t sprocket.

    -Air filter "box" was drilled for more air flow (Lean?)
    -Intake manifold ported
    -Exhaust manifold ported, pipe to rear wheel, no muffler (lean?)

    As it sits right now, partial throttle isn't smooth, it backfires alot, WOT is fine for a short period, then it just falls on it's face, sputters, then falls on it's face again.

    I'm guessing all this is due to it being lean? I did a quick WOT pull and pulled the plug and it was wet, however that's probably from the oil I'm guessing, can you read sparkplugs on a 2 stroke?

    I had a DIY muffler and it seemed to make it run better, my first question is, where can I buy a cheap (not $30+) muffler, quieter the better, and enough backpressure to fix this tuning problem would be nice...?

    Second, if this can't be fixed, would taking out the primary jet and drilling it be enough? Anything I should worry about (like it constantly dumping fuel)?

    Also, top speed sucks, but I'm 220lbs, 33T sprocket on a 20" wheel? or just go 27?

    (I've search extensively, but it seems every problem is a little different)

  2. arceeguy

    arceeguy Active Member

    Who "ported" the engine, and what are his qualifications for engine modification?

    As far as rich or lean goes, I've seen engines with rich low-mid speed, and lean high speed mixtures. Plug wet with oil, but lean bog near top speed and WFO.
  3. Khronokai

    Khronokai New Member

    The current owner of the bike, who's also my friend. I was there when he did it, it can't be port matched to the engine, since that's totally oval and the manifolds are round, however quite a bit was removed.

    As for qualifications, we both work on cars.

    It's disconcerting because I have no experience with 2-stroke, but from everything I've read, opening it up just leads to more air, leaning it out. I also know that with the DIY muffler it was running alot better, although not perfect.

    So before I buy it I need to know if there's some nice quiet/restrictive muffler I can run (everyone talks about them and posts pictures, but never say where they got it from), or whether I should just jet it. [EDIT] Either way it's getting a muffler, I need it for long commutes.
  4. arceeguy

    arceeguy Active Member

    This was just a "port match" at the intake and exhaust? Or were the ports enlarged in the piston bore itself.

    If it was a port match, then you are probably ok. Seen many engines ruined from people hogging out cylinder ports without regard to timing.

    It might be a good idea to get a stock muffler, install it and see how it runs. It'll be a good reference point.
  5. Khronokai

    Khronokai New Member

    No no, it was a "port match" (though as mentioned, we couldn't open it up THAT much to match the cyl. )

    Does anyone know of a "universal" muffler I can add to my pipe? I'd rather keep the extension which relocates the muffler to the rear wheel. :thinking:

    I've got a tight budget. lol
  6. arceeguy

    arceeguy Active Member

    Your ears will be the ultimate decider.

    You should be able to hear if the engine is running rich or lean and at what throttle positions and RPM.

    A free flow exhaust, along with a less restrictive intake would probably put you a bit lean at WFO, but you really need to listen to what your engine is telling you.

    If it runs/sounds stronger at 3/4 throttle than it does at full throttle, then you are lean.

    If it sounds like your engine is trying to cough up some phlegm, it is likely too rich.
  7. John Ryan

    John Ryan New Member

    Install a chainsaw carb and go! Best thing I've done to my bike!
  8. motorpsycho

    motorpsycho Active Member

    drilled holes in the air filter cover will not cause it to run leaner. but i high flow air filter might. If it has a straightpipe with no muffler/baffle, it will run a tad lean.
    my occ chopper has a carb stack with a high flow filter, a modified long pipe, with a modified muffler/baffle.
    i had to richen my main jet by going up to a # 72 jet. i am assuming that the stock jet was around a #70 and it was too lean. it did what you describe at w.o.t., it would bog and stumble, and fall flat on it's face at w.o.t. this is a sure sign og it being too lean.
    i think you are ok with the port matching as long as too much wasn't removed(which you already stated).
    mine has a 41 tooth sprocket and i am getting 32 mph top speed out of it.
  9. unior

    unior Member

  10. piecepatrol99

    piecepatrol99 Member

    about your muffler on a tight budget...

    Hi Khronokai. I see its been some time since your post, I hope this helps...
    You'll need:
    a piece of car exhaust pipe (diameter of you liking).
    Two pieces of stock plate to cover the ends.
    Two 3/4" OD copper reducers.
    Two 2" lengths of 3/4" ID pipe.
    A 1/4" stud or threaded rod approx 1" longer than the pipe, two nuts for the stud and a few sheet metal screws.
    And a bag of raw (without soap) steel wool.

    The steel plated will be cut to cover the ends of the pipe section. These pieces will be the muffler housing.
    Drill two matching holes in both plates. One 3/4" for the copper pipe and one 1/4" for the stud.
    Drill a hole in the side of the copper coupler with the copper pipe in side of them (kill two birds with one stone ;-) ).
    Place a set screw in the assemblies.
    Slide the copper pipes through the 3/4" holes you drilled in the steel plates. These will be the inlet/outlet of your muffler.
    Place the stud with a nut on it through the plate then through the piece of exhaust pipe.
    Fill the pipe with the steel wool (stretch and fluff first for best sound dampening).
    Place the other plate (with copper adapter inward and copper pipe outward) over the stud at the open end of the pipe piece.
    Tighten nuts at both ends.
    Connect to header and mount.

    You've just made a tunable custom muffler for about $15.
    Want more flow? Remove some wool...don't have eenough? Pack it tighter ;-)

    I'll be doing this soon my self using one muffler shell as an expansion chamber and gutting the baffles out the second and repacking it with wool. The outlets on both will be opened up from 3/8" to 3/4".
    I'll also be wrapping the entire length to further silence it...police cars are quick but you never hear them coming ;-)