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Discussion Starter · #1 ·
My carb is popping back through the carb. Ive' been told this is a lean condition and to change my power valves. My question is. How do you know when one is bad? You can measure vacuum, idle and other things on a carb but how do you "measure" power valve performance. How do you know when one is bad?
 

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They "normally" fail in the rich condition. It will puff black smoke big time at idle and cruise. If for some reason it wasn't opening and the diaphram wasn't torn, there would be a huge hesitation and "lean" popping. All this holds true for Holley's. Other brands have similar funtionality with different components and are less sensitive to a "backfire" failure.
 

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Michael,

Did this just start after doing some work or other work on your car??

Just curious cause if you don't see a horrific rich condition or an extreme lean condition as stated above then your looking at an ignition prob somewhere.

-Greg

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Discussion Starter · #5 ·
I just bought the car. It has an SB 406. No body knows about the motor but it puulls 15 inches of vaccum and takes pump gas. It has a Demon 650 carb. It pops back through the carb below 2500 when you hit the gas hard. Above 2500 it runs fine. I am just trying to tune it. It is getting better as I am moving up in squirter sizes but my friend said to change the power valeves too. So I will, but I don't know how to know if they are bad and he can't really explain it.
We are going to play with timing, but I want to know about the power valve thing firts. Kinda like on step at at time
 
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