power valve circuit myths

[Geoff2]

There is no siphon effect, that is one of the jobs an air bleeds does, introduce an air leak to stop siphoning.

[Robban 54]

Why do the IFR not take fuel directly from the floatbowl?
They can sit next to the MJ.

[jmarkaudio]

Why do the IFR not take fuel directly from the floatbowl?
They can sit next to the MJ.

It can and will run, but that's not the way the Holley was designed to operate. As the throttle blade opens from idle the t-slot takes away fuel from the idle circuit, as the blades open farther the mains start and the t-slot tapers off, in some cases backfeeds as a bleed. If the idle/transition circuit draws from the mainwell it doesn't shut off.

[jmarkaudio]

If the power valve opens at 8.5 and he's idling at 6, the valve will sit there open but not flowing until there's enough depression to draw from the boosters, correct?

With the power valve busted or open , it can make the idle circuit richer ,, those that dont believe this must not have ever had it happen to them ,, fuel is not coming out of the boosters but the exhaust will burn your eyes up . Ive been called several bad names on here for claiming this ,, but its real

It will not affect it open. I did this to show that a PV that is either open or closed at idle has no effect on idle fuel mixture. The carb is one of a pair of external boost referenced PV carbs, internal vacuum supply is plugged. Engine RPM was brought up after and confirmed the PV operation. Only a bad diaphragm or leaking PV gasket will bypass fuel to the vacuum side of the PV and pull it into the engine. Check the you tube video.

https://youtu.be/jlp-Q_3fzKM

[Robban 54]

If the idle/transition circuit draws from the mainwell it doesn't shut off.???
Do you mean floatbowl.
There must be a difference if the power valve is broken or open.
I have noticed a difference in idle AFR after changing the MJ no other changes.

[levisnteeshirt]

If the power valve opens at 8.5 and he's idling at 6, the valve will sit there open but not flowing until there's enough depression to draw from the boosters, correct?

With the power valve busted or open , it can make the idle circuit richer ,, those that dont believe this must not have ever had it happen to them ,, fuel is not coming out of the boosters but the exhaust will burn your eyes up . Ive been called several bad names on here for claiming this ,, but its real

It will not affect it open. I did this to show that a PV that is either open or closed at idle has no effect on idle fuel mixture. The carb is one of a pair of external boost referenced PV carbs, internal vacuum supply is plugged. Engine RPM was brought up after and confirmed the PV operation. Only a bad diaphragm or leaking PV gasket will bypass fuel to the vacuum side of the PV and pull it into the engine. Check the you tube video.

https://youtu.be/jlp-Q_3fzKM

Does to

[jmarkaudio]

If the idle/transition circuit draws from the mainwell it doesn't shut off.???
Do you mean floatbowl.
There must be a difference if the power valve is broken or open.
I have noticed a difference in idle AFR after changing the MJ no other changes.

The Holley 4 barrel was designed to pull idle/transition fuel from the mainwell so it does shut off when the mains start. It can even become an air bleed at the bottom of the well when draw thru the booster is high enough.

Pulling from the flat bow directly it won't shut off.

Open PV will not richen the idle mixture, as the video link demonstrated, a blown PV diaphragm or leaking PV gasket will. Levi's carbs will richen at idle because the blades are so far open the boosters are flowing...

[mopardave]

Mark i watched your vid. Maybe i'm wrong here, but when you introduce vacuum to the pv it closes the pv. Removing vacuum opens it.

[jmarkaudio]

Mark i watched your vid. Maybe i'm wrong here, but when you introduce vacuum to the pv it closes the pv. Removing vacuum opens it.

Yes. Either way the idle AFR did not change.

[mopardave]

OK, i understand.