Is my 2-stroke fried???

Discussion in '2-Stroke Engines' started by Masor, Jun 13, 2011.

  1. Masor

    Masor Member

    Hey everyone, I had just finished building my new bike and I have been riding it for 3 months. During the three months I have noticed an increase in 4-stroking when I ride. It used to be mostly at top end (WOT). Now it is four stroking all the time? I cant seem to fix it. I put an in-line fuel filter on, I tweaked with the c-clip in the carb on every position, and it doesn't work? I'll include a picture if you want to point out any concerns.
     

    Attached Files:


  2. HeadSmess

    HeadSmess Well-Known Member

    read up on jetting. :)

    im sorta guessing your plug is black as um... black stuff :)

    n pulling the exhaust n seeing if its all gummed up is another point..
     
  3. HeadSmess

    HeadSmess Well-Known Member

    n nice bike btw...who's responsible for that fabrication?
     
  4. Masor

    Masor Member

  5. nwohater

    nwohater New Member

    I've never heard the term 4 stroking, please explain. If you haven't been mixing too much oil in your gas then like was said check the plug, check exhaust isn't plugged, then make sure spark is strong and plug fires strong still when warm. Often when an ignition is going bad it'll get weaker as the bike warms up. The plugs that come with these engines aren't always the best either.

    The other thing it could be is if your reeds are bad, cracked, gummed up, or have something stuck in them. If you've been using gas that may have had even the tiniest bits of dirt or grit or anything in it from say a can for a lawnmower, you might want to check the float valve on the carb to be sure it's not stuck.

    2 strokes fairly new like yours aren't likely seriously damaged, especially if it turns free and you have been using 2 stroke oil, and they're cheap and easy to fix you just have to narrow it down. If it has good compression then the reeds are fine, and the piston/cylinder is fine, if it has good strong spark when warm then the plug and ignition are likely fine.

    btw cool bike
     
    Last edited: Jun 14, 2011
  6. Al.Fisherman

    Al.Fisherman Active Member

  7. motorpsycho

    motorpsycho Active Member

    once again, the clip position on the jet needle does nothing at w.o.t. it only affects the mixture from idle to about 3/4 throttle.
    these engines do not have reed valves (as nwohater mentions).
    a stuck float will not cause 4 stroking, a stuck float will result in either A. the engine will not get any gas and will not run, or B. the carb will flood over and spill fuel all over the place.

    first thing i would do is make sure that the choke isn;t partially closed. the choke on an n.t. carb is very simple and they can vibrate loose. If you have a cns carb, the choke is more like an air bleed and you will have to make sure that it's closing all the way when you turn the choke off.
    then, i would pull the float bowl off and look at the main jet. the main jets on these carbs have been known to vibrate loose and fall out into the float bowl.
    check your air filter, make sure it's not plugged up.
    if your engine is 4 stroking you are not getting enough air....like the choke is closed, air filter plugged or the jetting is too rich (too much fuel, not enough air).
    i have found that 80% of getting these engines to run right is in the tuning of the carb (re-jetting). also, a better exhaust will help you out too, like an expasion chamber, the stock mufflers plain suck, and they will plug up over time.
     
  8. Masor

    Masor Member

  9. Masor

    Masor Member

    motorpsycho, I adjusted my float because it used to overflow, now its fine. And as for the choke, I took it off because it would loosen after every ride and shut my bike down. I screwed in both of the jets fairly tight and put a smaller main jet in. I don't run an air filter anymore; instead i built a scoop, like on some cars, and put a screen at the opening. What I'm suspecting at the moment is either the spark plug, or the fact that my carb is not level. Or maybe because i have 850 miles on it.
     
  10. motorpsycho

    motorpsycho Active Member

    both jets?
    these carbs only have one jet.
    if you're running a scoop with a screeen that will eliminate the plugged air filter theory.
    your carb not being level could possibly have something to do with the problem. but if the carb is in the same position now as it was when it didn't 4 stroke, then i doubt that it;s the problem.
     
  11. tone2crazy

    tone2crazy Member

    you need more then just a screen to filter the air
     
  12. Masor

    Masor Member

    Oh sorry about that, I meant the main jet.
     
  13. q999

    q999 Member

    air filters are for those who are scared to scrape up their cylinders with sand.,we don't need no filter. lol
    remember your plug may need cleaning, after 4 stroking, and check the gas make sure it's not bad.
    good luck.
     
  14. Masor

    Masor Member

    These pictures are of my piston since last cleaning it 3 months ago, and of my spark plug after 5 minutes of riding. There's also one picture and I'm concerned about the marks at the top...
     

    Attached Files:

  15. motorpsycho

    motorpsycho Active Member

    you need to move the piston down and look at the cylinder wall.
    if there are any scratches from dirt, they will show up there.
    the top of the piston will build up with carbon over time, but yours looks really clean compaired to a lot of them.
    the marks on the edge of the combustion chamber is where the gasket seals against it.
    I have no idea why those marks are there, but the piston will never contact that area. the area to be concerned about is the dome where your spark plug screws in.
    you could try to sand off those marks on the edges and it may help the head gasket seal better.(and if you remove enough it will up your compression ratio for a little more power). but, you have to be careful not to remove too much material from that area. this is the same as milling the head. I have never done it so i have no idea what a safe amount to remove would be.
    those marks could be from the machining process, but they look pretty rough.
     
  16. HeadSmess

    HeadSmess Well-Known Member

    lay the sandpaper on a sheet of glass if youre gunna sand the head. you need it to be flat. squares (parallel) is also nice but not too much of a concern on a single cylinder cheapie... just flatness hence sealing is.
     
Loading...