Engine 4 Strokes at Cruise

Discussion in '2-Stroke Engines' started by Randall, Sep 1, 2016.

  1. Randall

    Randall Member

    Can anyone help me with a 4 stroking issue. It accelerates just fine but when I turn the throttle back a bit to cruise it 4 strokes really bad. I have this carby: http://www.bikeberry.com/engine-kit-parts/fuel-components/66-80cc-high-performance-carburetor.html. An open pipe (for now). Thinking it might be the jet or the float. But I recently checked the float for damage and none found. It just started doing this after I put on the straight pipe. I put some copper scouring pad material in the pipe to tone it down and give it a little back pressure, but that didn't work.
     

  2. Slogger

    Slogger Member

    That's sold as an RT carb some places. It can use the same main jets as the NT carbs.
    Dellorto 5mm ones, if I remember right. SBP sells them in sets or singly for a few dollars each.
    You can try one step smaller (leaner) main jet. I tried one of those carbs and it was never right on the top and the bottom at the same time, other guys like them just fine. It depends on your engine's set-up, I guess. I got mine for less than $30, that site might be a little high on something.
     
    Randall and gary55 like this.
  3. Frankenstein

    Frankenstein Active Member

    What pipe did you use before? Did you figure this problem out in the last 3 weeks since you posted?
     
  4. KCvale

    KCvale Motorized Bicycle Vendor

    You can't 'tune out' a mistake like exhaust...
    You never want to run a straight pipe a on a 2-stroke, and why you are having issues.

    2-strokes don't have valves.
    You are literally spewing power and raw fuel out on the road when you ride!

    Follow the green fuel in this vid.

    With a strait pipe all that green gas/air/oil mix escaping the engine just goes out the end with a straight pipe and on the road!
    An expansion chamber like the one shown has a back-force wave timed to shove the fuel mix back in just in time for firing for a bigger punch and more power, not to mention no more puddles of oily fuel on the ground wherever you park.



    [​IMG]
    The stock pipes do an OK job of producing back pressure to shove the unburnt fuel back in the cylinder, but a tuned expansion chamber exhaust does it much better, it works like a reverse turbo charger and gives you the best power boost and my #1 rated single upgrade there is for a 2-stroke engines.

    That should set ya on the right track ;-}
     
  5. gary55

    gary55 Active Member

    I'm at 5200 ft. and have found these carbs. hard to tune to a sweet spot. When you lean them out enough to stop 4 stroking you have to set the idle high. You may have better luck at 2200 ft.. Try a #68 nt jet from SBP and keep an eye on your plug to make sure it's not running to lean.
     
    Randall likes this.
  6. gary55

    gary55 Active Member

    I also agree with KC, and if your going to put on a expansion chamber you should wait till it is on before fine tuning your carb.
     
    Randall likes this.
  7. Randall

    Randall Member

    Yeah I think running a smaller jet would help the situation.
     
  8. Randall

    Randall Member

    It was the stock pipe with out the silencer.
     
  9. Randall

    Randall Member

     
  10. Randall

    Randall Member

    This is the current setup. The oil leak is coming from a bad welding job. My first weld in over 20 years. Getting better as the Motorized Bike Stand can attest. IMG_20160928_171910337_HDR.jpg LOL
     
  11. KCvale

    KCvale Motorized Bicycle Vendor

    Well, it's your bike, jet it all you want, but that crap exhaust you have will still be there wasting fuel and power.
     
  12. Slogger

    Slogger Member

    KC's right about the megaphone pipe not working good on a cg. I actually like the stock mufflers since the engine runs ok and is very quiet, but I'm not digging for extra hp out of the little thing, just enough to cruise easy at 25, top out at 30+. It's perfect for that just how it is.
    Light weight, too. and Free. Hard to beat.
     
    Randall likes this.
  13. gary55

    gary55 Active Member

    Hay Randall. You actually did tell us you were only running that pipe for now in your first thread. Surely no harm in experimenting. That's what I'm doing.
     
    Randall likes this.
  14. Randall

    Randall Member

    Well it has LOTS of power when it's not 4 stroking. I wish I had a Go-pro camera mounted on my helmet
    to show you and others how it does going UP my gravel hill driveway and the flats.
    The "crap" exhaust is only temporary any way. Thinking seriously about getting Jaguars CDI.

    https://www.dieselnet.com/tech/air_scavenge.php
    http://www.dragonfly75.com/motorbike/4stroking.html
    http://www.mopedarmy.com/wiki/Four_Stroking
    http://motoredbikes.com/threads/four-stroking.47602/#post-412157 : --- I had forgotten about this one.

    To fix a four stroking problem:
    • Clean your air filter to remove any blockage - this may solve your problem.
    • If you've cleaned your air filter, and you're still four stroking, you will need to put a smaller main jet in your carburetor.
     
  15. gary55

    gary55 Active Member

    Jag's cdi's work real good. I have 2 of them. With the cdi and a good expansion chamber you might not need to mess with the carby.
     
    Randall likes this.
  16. Randall

    Randall Member

    Thanks
     
  17. Randall

    Randall Member

    Yeah, I will keep tinkering with it. Noob learning curve. If it needs an expansion chamber, so be it:
     
  18. zippinaround

    zippinaround Active Member

    Since you have a welder you should try making jags pipe! I made one (not exactly to jags spec) and it made a world of difference , recently I swapped back to a stock pipe while I was adding a belly stinger to my "jag" pipe and it was total crap , engine ran terrible with no torque.
     
  19. Randall

    Randall Member

    Okay, I will take a look at it, thanks.
     
  20. Randall

    Randall Member

    The other thing is as far as the noise goes, in my little town, most auto drivers don't pay attention driving around and will pull out right in front of you. I have found the louder you are the more they will notice you. It'so bad here that I even had a US Postal delivery truck blow my school bus stop sign the other day. My bus has an air horn that works VERY well. :D
     
Loading...