Why does my 2 stroke carb have a bowl vent AND an overflow tube?

Discussion in 'The Garage' started by frascati, Oct 4, 2019.

  1. frascati

    frascati Adventurer

    Mar 23, 2018
    The overflow tube is always open to atmosphere at the top of the tube (above the fuel level).
    The bowl vent is always open to atmosphere at the carb body above the float.

    Is this just redundancy in case one gets clogged? Should blocking one or the other have any effect at all on fuel flow as long as one of them is clear? (eliminating neg or pos air pressure in the bowl)?
  2. spafxer

    spafxer Long timer

    Mar 12, 2007
    bottom one allows bowl to overflow onto the ground if float bowl overfills.

    bottom one is not always open, when crossing a stream the fuel drain covered by water will kill the engine instantly. DAMHIK

    If you have the upper opening it will still allow atmospheric pressure to deliver fuel through the jets.
    spokester likes this.
  3. unfocused_adventure

    unfocused_adventure Not my circus, not my monkeys... Supporter

    Oct 1, 2019
    Auggieland FL.
    Get yourself a couple of these 2 cycle fuel filters from where ever and this keeps em from getting clogged.

    You need them BOTH breathing. Ones for if the float is stuck open causing the bowl to overfill and flow out the tube or the engine will fill up( not good ) the other is a vent so the float bowl doesn't vacuum lock causing fuel starvation. we call this a "dirty" air/vent line as debris can end up in the float bowl.

    lnewqban likes this.