Carburetor power valve question (2 Viewers)

[devo]

Do all Asian 2 barrel carbs for the 2F have power valves? I’m noticing that some carbs do not have the vacuum port at the top front and some do? My minimal understanding is that it takes some manifold vacuum to keep the valve closed and negative at open throttle to activate it?

 

[devo]

Maybe I found the answer? But, if the carb has a port for vacuum to keep it closed on some models, why is it not necessary on all carbs. Is the port for vacuum to keep the PV close only on newer emissions carbs?

Thread 'Aisan Power Valve Circuit'
Aisan Power Valve Circuit - https://forum.ih8mud.com/threads/aisan-power-valve-circuit.989037/

 

[mattressking]

Yes it exists on all 2F carburetors. The vacuum source for the Power Valve is the rifled carb body screw on the base of carburetor. Once....3inHg of vacuum ( I believe) hits the manifold, the Power Piston is pulled away from Power Valve. As vacuum drops, the spring overpowers the reduced vacuum and begins to press on power valve, providing fuel from bowl to carb nozzle(s).

 

[devo]

Thanks Nate. I do follow what you’re saying and it is explained clearly in my post #2. On this 1983 carb I have at the top front there is a port that goes to vacuum in order to keep the PV closed. Is this simply a redundant vacuum port for newer emissions carbs or is the vacuum port in the carb body not used? If I were to cap the upper vacuum port off will the power valve function properly? I don’t see that upper vacuum port on some older carbs and general market carbs.

 

[65swb45]

Yes it exists on all 2F carburetors. The vacuum source for the Power Valve is the rifled carb body screw on the base of carburetor. Once....3inHg of vacuum ( I believe) hits the manifold, the Power Piston is pulled away from Power Valve and fuel flows from bowl to carb nozzle(s).

Exactly the opposite.

Vacuum keeps the power piston retracted into the air horn. When vacuum drops sufficiently, the spring behind the piston, along with gravity allow the piston to fall, press on the power valve and open it.

Even a cursory examination of the power valve would reveal that the valve is closed in the UP position.

 

[sggoat]

Thanks Nate. I do follow what you’re saying and it is explained clearly in my post #2. On this 1983 carb I have at the top front there is a port that goes to vacuum in order to keep the PV closed. Is this simply a redundant vacuum port for newer emissions carbs or is the vacuum port in the carb body not used? If I were to cap the upper vacuum port off will the power valve function properly? I don’t see that upper vacuum port on some older carbs and general market carbs.

Think both previous posters(Mark and Nate) are saying the same thing from different perspectives--bottom line is when vac drops sufficiently, the power valve opens and gives more fuel=more power

 

[devo]

Yes @sggoat that is true. But why on some carbs that vacuum is provided through the carb body only and on others through the valve body and a port on the air horn?

 

[mattressking]

Exactly the opposite.

Vacuum keeps the power piston retracted into the air horn. When vacuum drops sufficiently, the spring behind the piston, along with gravity allow the piston to fall, press on the power valve and open it.

Even a cursory examination of the power valve would reveal that the valve is closed in the UP position.

Mark, we are saying the exact same thing, I just tweaked one portion to make it easier to understand.

Yes @sggoat that is true. But why on some carbs that vacuum is provided through the carb body only and on others through the valve body and a port on the air horn?

Note that the center vac port on the carb air horn is to provide full manifold vacuum to external sourcess....for example, choke breaker on later 2F carbs.