Carb power valve operation question

Arrowglassrestorer

Seaman Apprentice
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Feb 11, 2017
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31
Rebuilding my mercrusier 2 bbl carb 1389-9562. In the base of the bowl there is a power valve and in the air horn there is a spring loaded piston that is supposed to retract under vacuum thus closing the power valve. The problem is that I can't get it to retract if I put vaccum in the hole leading to the piston. However the piston is easily moved in and out with my finger. This carb has very little use(been on shelf) and the piston should not be worn out. I don't believe there are any seals inside the piston to wear out. While the power valve was included in the rebuild kit there was no rebuild for the piston in the horn. If I install the carb as it is the power valve will be open all the time since high vaccum doesn't move the piston up to allow the valve to close. Any suggestions
 

Arrowglassrestorer

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Feb 11, 2017
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Curently it pushes very easy and will fit right back out as soon as you slid your finger off. My question is , how do you test if the vaccum is pulling it in.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
What are you using for a source of vacuum? How you sealing it to the vacuum passage? Are you applying the vacuum to the proper passage. The one near the power valve in the cover is a vent, and will not raise the piston.
 
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Arrowglassrestorer

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Feb 11, 2017
Messages
31
That could be my problem. Maybe I am pulling vaccum from the wrong port. Currently I am pulling vaccum front the small round hole just inside the horn. The hole is less than a 1/16 in diameter and if you look into the hole you can see the brass piston move as you push down. Am I testing thru the wrong port?
 

alldodge

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Mar 8, 2009
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40,581
Am I testing thru the wrong port?

I don't know, this like all cabs need to take everything apart in order to see what needs work. Understand so far your not able to get the piston out, but it has to come out to repair. It may not need to come out but so far your not able to draw it up with a vacuum, so the seal may be leaking. Another thought is your not able to draw enough vacuum fast enough to move it, again don't know.
 
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