backfiring on cold starts

Discussion in '2-Stroke Engines' started by tone2crazy, Jun 14, 2011.

  1. tone2crazy

    tone2crazy Member

    does anyone else have this problem? sometimes in the morning when i first hop on it, the engine feels like its not working. then i have to pedal a good distance. til the engine backfires with a loud pop. and the engine starts like usual.

    im asumming its either the muffler. which is a 4 stroke muffler. and retarded to put on a 2 stroke imo. but thats most likely due to the epa. or the horrible electric system.
     

  2. motorpsycho

    motorpsycho Active Member

    do you use the choke when you start it?
    2 strokes can't backfire.
     
  3. tone2crazy

    tone2crazy Member

    i dont know what its called but it is a loud pop. and no i dont use the choke. it wont start if i have the choke on. and my plug is mocha so i know the tuning is good.
     
  4. motorpsycho

    motorpsycho Active Member

    does your carb have a little primer button on the left side?
    do you use it?
    if not, try pushing it a few times after you turn the gas on, this will put some extra gas into the cylinder which helps get the engine started.
    i can start my engine within 5-6 feet after i get the bike moving. I coast down my driveway and pop the clutch....starts every time.
     
  5. tone2crazy

    tone2crazy Member

    yeah i always prime it. and this doesn't always happen. just every so often in the morning.
     
  6. adrian101

    adrian101 Member

    Are you sure 2 strokes don't backfire? Reason i ask is because mine has also done it before. I was thinking it was my exhaust because mine started backfiring once i changed from the stock exhaust to the Street pipe(poo poo).

    It's only done it once but I'm pretty sure it was a backfire
     
  7. HeadSmess

    HeadSmess Well-Known Member

    check the exhaust gasket. take a file to both the cylinder port (remove studs :thinking: ) and exhaust flange. youll see the high spots on the first stroke. get em flat. mainly the flange.

    ignore it? or even, :bowdown: REVEL :bowdown: in it? loud pops are cool :whistling:

    the 4 stroke muffler, while affecting overall performance, will still muffle. just your engine wont make much power. not that stocks any better :jester:



    so. back firing is usually caused by a leak in the exhaust system. but two strokes rarely do it.

    what can happen in them is the mixtures TOO rich, and the unburnt fuel has to accumulate somewhere, right? and what happens when you have a big chamber full of unburnt fuel and air and you apply a flame?? pop :D

    the engine has to actually get rid of excess fuel until the mixture is lean enough to ignite.

    remember, cold fuel doesnt vaporise. liquid fuel doesnt go bang. it has to vaporise to do what we want :)

    also, idea to check the wiring for good earths etc. a weak /intermittent spark can do it tooo... try a faulty kill switch on a 4 cyl moto for backfiring!

    heat the carb up a bit with a hair drier?
     
  8. motorpsycho

    motorpsycho Active Member

    yep a 2 stroke can't backfire because there are no valves.
    a backfire is normally caused by an exhaust or intake valve that fails to open, or ignition timing that is way off causing the spark plug to fire at the wrong time when the valves are in the wrong position.
    this can only happen on a 4 stroke.
    a 2 stroke will either run or it won't run.
    popping could just be excess fuel built up in the crank case / combustion chamber and when the spark plug fires, it ignites more fuel than normal which will give you a bigger explosion....or "pop" out the exhaust.
     
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