Carby Running rich but boggs if fuel/air screw is moved out

Discussion in '2-Stroke Engines' started by Motocruiser, Apr 27, 2011.

  1. Motocruiser

    Motocruiser Member

    So ive gone through my first tank of gas and it only seems to want to run if the fuel/air mixture screw is all the way in, which causes the engine to run rich from the looks of my spark plug grey/black. Any suggestions for remedy?

  2. DuctTapedGoat

    DuctTapedGoat Member

    Adjust the clip on your throttle pin, then fine tune the idler screw.
  3. motorpsycho

    motorpsycho Active Member

    are you sure that your carb has an air-fuel mixture screw and not just an idle screw?
  4. one thing i have found out with my first build is that oil mixture makes a big difference too. i was running 16:1 lucas semi synthetic. and i have been having problems with it running rich. i even bought the dellorto jets. and messed with the needle adjustment alot. but once i used 20:1 oil mix, the engine ran so much better! and im sure if i go with 22:1- 25:1 it will run even better yet. you still have to screw with the needle clip, and jets for awhile though to get everything perfect. if thats what you are looking for. really though my sd stinger ran good enough to ride out of the box. but i like to fine tune things..
  5. Motocruiser

    Motocruiser Member

    @DuctTapedGoat: i was thinking i should adjust the needle but wasnt sure. I feel like i shouldnt have to run with the air/fule mix screw all the way in.

    @MotorPsycho: I have the CNS stock carb forgot to mention that little piece of info. LOL!

    @Back2theborsal: I'm running 18:1 oil/gas. That mixture shouldn't have anything to do with the carb getting to much fuel and not enough air.

    I've heard so many people complain about the CNS carb and thought maybe I should go with the Speed or NT carb due to their simplicity. They look like clones of the Dellorto SHA 12mm carb that self adjusts. I appreciate the input, like I said I'll have to try adjusting the needle down shutting off excess fuel delivery. I'll post what I find. Just wanted to get it taken care of before JAGUAR's CDI coil combo comes, and the new sprockets. Just a little FYI I've gone through 1 1/3 tanks of gas and finally feels like its got more power. I hit 31.4 mph with my 24" (20") wheels and a 44t sprocket. Looking for 40 top end so I can cruise at 30-35 with traffic. I'll get some pictures and videos up soon. Stay tuned!
  6. motorpsycho

    motorpsycho Active Member

    lets not forget that oil-fuel ratio is way different than air-fuel ratio.
    air -fuel ratio is make your engine run lean or rich.
    oil-fuel ratio is just that and has nothing to do with the air-fuel ratio.
    more oil = more smoke, more gunk on the plug, more lube for the bearings and a cooler running engine.

    Less oil = less smoke, less gunk on the plug, less lube for the bearings and a slightly hotter running engine.

    too much air to the amount of fuel= lean conditon (too much air not enough fuel), this will make your engine run really good and make a ton of power, rev really high, idle high, possible w.o.t bogging, but you run the risk of melting the piston or causing a bearing to lock up. the engine will run HOT!

    too much fuel to the amount of air = rich condition (too much fuel and not enough air) sluggish throttle response, bogging, more smoke out the exhaust but not from oil, hard starting, 4 stroking and low performance.
    also, the air quality where you live will have a lot to do with the air-fuel ratio that you need. an engine that runs good in new york, will probably run like **** in florida.

    Personally i run all of my 2 strokes at 32:1 oil-fuel ratio because it's what works for me.
    Last edited: Apr 28, 2011
  7. Motocruiser

    Motocruiser Member

    Late 60's early 70's American Flyer I inherited from my Grandfather. All original except for crank, wheels, and handle bars.

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