Engine Trouble engine wont idle. will only start on full throttle.

Discussion in '2-Stroke Engines' started by def215, Mar 17, 2014.

  1. def215

    def215 Member

    ok guys. im having a bit of trouble with my engine on my most recent build.

    so i have a homelite bandit sx-135 on my bike set up as a friction drive. i had my bike out the other day and it ran like normal. all of the sudden, i come to a stop and let it idle and it cut out. i tried to restart it and get it running but it wouldnt. i then gave it about a 1/2 throttle and it fired up, then i let off to let it idle and it died again.

    i then tried riding it as a normal friction drive, which it would normally fire up after a few cranks, but it didnt, i have to give it more than 1/2 throttle and it will start up and rev out fine up to its top speed. i have no clue whats going on. ive played with the low and high jet screws in every position and still nothing.

    im out of ideas and im turning to you guys for some help.

  2. dchevygod

    dchevygod Member

    Try and start it normally without any throttle and pull the spark plug, if its dry you have a Plugged low speed fuel circuit. Need to clean out the carb at least, may need a gasket kit and worst case new carb time. I had a real long write up explaining everything but my phone wouldn't post it. Hope this helps.
  3. keatonx

    keatonx Member

    When you slowly let off the gas until it stalls does it start to run rough and slow (rich) or does it get smooth before it dies (lean)? You can tell from the sound
  4. dchevygod

    dchevygod Member

    He was riding when it happened, I think the carb sucked up a piece of junk while he was at a stop. He has a pumper carb not a float bowl. There is no way for it to be a rich fouled plug I don't think
  5. keatonx

    keatonx Member

    On my (very worn) weed eater bike with a MTD/ryobi 31cc (which btw has a sx135 carb) I often have to throw it on full choke so it stumbles, then flip off the choke to start it because it sometimes doesn't get enough gas to start. And when I'm cruising at low speed it will sometimes lean out and die, so I need to flip on the choke to start it up and it's fine after that. Idk what is causing this, probably the somewhat bad carb diaphragm or leaking crank seals (Bearings are bad, I can wiggle the the crank a few mm's in every direction)

    So basically, when it dies out, throw it on full choke and don't give it any gas, and see if it fires up for a moment. If it does then I'd first check for a stiff carb diaphragm. Then an air leak (or even cracked intake block since you have a piston port).

    And even if your diaphragm seems good, it's always a good thing to replace it because they need to be extremely flexible. Mine also seemed to be sticking in the full-out position, which may have been my problem.
  6. keatonx

    keatonx Member

    I don't mean a fouled plug; that would make it not want to start at any throttle position.
    Just regular richness making it want to die at low speed. It isn't usually the case on weedeater engines but it's a fairly straightforward test to see if it's lean or rich (start it up and listen).

    It could suddenly become rich if the carb diaphragm got stuck in one position, or the carb was semi plugged when he tuned it, and then all the junk in the carb loosened up and came out causing the adjustment to be rich.
  7. dchevygod

    dchevygod Member

    If the diaphram was stuck open it wouldnt fire at half throttle either. He says is revvs like normal above 1/2 throttle. If it were rich it would fall on its face especially in the higher rpms. I've had this exact same issue on my cy290 with a walbro 257 carb. It was a bear to Pull start and wouldn't idle. Cleaned the carb really well and it was back to normal. These carbs are great if you know how to tune the diaphragm pump lever for your motors fuel demand. If the height is low or high it will cause rich or lean conditions thru out the rpm range.
  8. BigBlue

    BigBlue Active Member

    Carb issue or a plugged muffler.

    AKA: BigBlie
  9. def215

    def215 Member

    thanks for the help guys!

    i finally got time to mess around with my bike and i tore down the carb and shot it with carb cleaner and also let it soak carb cleaner and that seemed to do the trick. it holds idle fine and revs out like normal again. now its only up to me to tune this thing correctly to run...lol

    i really appreciate all the help. :grin5:
  10. dchevygod

    dchevygod Member

    I called it. Plugged low speed circuit. You may want a pro to tune the carb while its in running condition to adjust the diaphragm lever for your fuel demand. It makes worlds of difference.