taco eater :
Bairdco from Midway City, CA United States
Every closed jet I've used on all my CPs I've had to drill the closed jet. I don't know why I don't just buy the open jet.
When closed, there's very little response from the air adjustment screw, and the carb runs rich, requiring substantially small main jets, for example, 75 main closed, 90 main open.
The smaller jet and closed air jet gives less power, and less fine tuning ability.
But that's just my experience in 5 bikes with 5 different engines...
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Good good
September 1, 2022
taco eater :
Jacob Fulton from Minneapolis, MN United States
I put this in my carb and my bike seems happy.
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Is this important? This is what polini has to say
July 18, 2022
taco eater :
@Kickstandbois from Grand Rapids, MI United States
Close air brake jet: 2 stroke atomizer type working as an atomizer without holes
Open air brake jet: the atomizer holes work and make the engine weaker.
Had to drill it open 
Good good