Carb pops

Discussion in 'Off Topic' started by yota89, Dec 30, 2014.

  1. yota89

    yota89 Enthusiast

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    Hey guys need some help on my mikuni 40s my carb pops when throttle release
    and also 2 carbs wet with fuel and the other 2 are dry 180 main 57.5 air 140 fuel and idk the Venturi size PLS help thanks
     
  2. B.Y.E.

    B.Y.E. Toyotaholic

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    Have you syncronized them?
     
  3. yota89

    yota89 Enthusiast

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    Yes i have syncro them their at 7
     
  4. B.Y.E.

    B.Y.E. Toyotaholic

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    Popping Is a sign of lean condition. Kinda confused on your jetting mentioned. Is it: 180 main, 140 main air and 57.5 pilot? If so that jetting is very lean on the air side. Simple rule of thumb on mikuni's is 30-50 increments bigger on main air than main fuel. Example: 150 main/180-200 main air.

    57.5 pilot is ok, air screws at the base of carb should tune it out once idle/vacuum (7kph) is achieved. You'll have to adjust them (air screws) one at a time. Idle and vacuum will change as you go so adjust that as you proceed to each airscrew. *note: disconnect throttle dog bone during this procedure as you want to be sure each carb arm is sitting on it's own idle screw.

    Fuel pressure not to exceed 4-1/2 psi... Stock manual or Napz electric pump works perfect at 2-1/2psi...

    Good luck! Krrrroooooook krrrrooooooook!!! :eek:
     
  5. tacobo670

    tacobo670 Addict

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    solid chelu!
     
  6. yota89

    yota89 Enthusiast

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    I recently rebuilded my carbs and i used 165 on the bottom of the shaft and 180 on top i still cant seem to fine tune it im ordering 200 jets for the top shaft what seems to be going wrong i tried to resync them down to 5 but its like it doesnt move thanks B.Y.E pls fill me n more carbs are sluggish but when it opens it wants to go
     
  7. tacobo670

    tacobo670 Addict

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    chokes/venturi's ?
     
  8. yota89

    yota89 Enthusiast

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    Venturi's are maxed out wheres the chokes location?
     
  9. tacobo670

    tacobo670 Addict

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    idk. im not too familiar with carbs lol sorry lai
    i guess some people call them chokes or venturis but they do the same thing, taper off or "choke" down the air flow.
    try go a few sizes down. maybe too much air/fuel, and no velocity. u need the velocity for the air/fuel to mix properly. just an idea before u go spend more money nai.
     
  10. yota89

    yota89 Enthusiast

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    Venturis: how do i check on the size?
    pilot jets: 57.5
    main air jets: 180
    main bleed pipes: T
    main jets: 165
    pump nozzles: 40
    starter jets: 130

    My jetting
     
  11. B.Y.E.

    B.Y.E. Toyotaholic

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    Can you post pictures?

    Here's a guide if your not sure what are Venturis... Mikuni Parts List & Diagram

    There are lots of little things that add up to poor running carbs, especially used carbs with unknown history. There are different types of 40's and they used different emulsion tubes and jets, some used air bleed pipes some did not. That website has the ID diagram also... :cool:
     
  12. yota89

    yota89 Enthusiast

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  13. yota89

    yota89 Enthusiast

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  14. B.Y.E.

    B.Y.E. Toyotaholic

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    Cool, air jets look correct. Besides the popping, id be more concerned on the "wet" cylinders. Fuel pressure?
     
  15. yota89

    yota89 Enthusiast

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    I regulated it to 2 1/2 fuel..idk why is it still
    Sluggish and popping
     

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