Power Valve question

[moparmarks]

Yes run a 4.5 in the secondary too.

 

[Moparnocar]

I know this is a very old post but wanted to ask about the second power valve on the secondaries. Ive never had a carb with both of them, I've only had them in the primary and there wasn't even a spot for one in the secondary. My new double pumper 750 has both front and rear. If my car is pulling 9hg of vacuum at idle (big cam and a 4spd with idle at 950) I would normally run a 4.5 power valve in the primary but what would I do for the secondary? Would that be the same or would I go slightly smaller like a 3.5 or 2.5?

I had the same, I ran a front pv, then plugged the rear, and went up a few sizes. I never tried no front pv.

 

[65_Satellite]

If they were the same, keep them the same.

I’ve never had a carb with both power valves. The new carb has a 9.5 and 6.5 from the factory but those are both too big. I know I need a 4.5 in the front but wasn’t sure how to set the rear because I’ve never had to

 

[moparmarks]

Ya double pumpers have a secondary PV and vacuum secondaries don't. Some delete the PV and bump up the jets. I've never done that myself. Funny that Holley doesn't recommend doing that but they make a PV plug.

 

[hunt2elk]

I know this is a very old post but wanted to ask about the second power valve on the secondaries. Ive never had a carb with both of them, I've only had them in the primary and there wasn't even a spot for one in the secondary. My new double pumper 750 has both front and rear. If my car is pulling 9hg of vacuum at idle (big cam and a 4spd with idle at 950) I would normally run a 4.5 power valve in the primary but what would I do for the secondary? Would that be the same or would I go slightly smaller like a 3.5 or 2.5?

Your power valve should be determined by what your cruise vacuum is, not the idle. The power valve won't be in the circuit at idle, unless something is messed up on your carb. I have a motor with 8" idle vac, and cruises at 16. I run a 8.5 PV in it. Even with a 4-speed and normal driving, it doesn't open earlier than I want.
I have never seen a carb with a valve in the rear. Are you certain it is not just a plug? I thought those were for a specific application?

 

[moparmarks]

I have several DP's with a secondary PV. That is interesting about how you rate a PV. Maybe that is what I doing wrong.

 

[Splangj]

Your power valve should be determined by what your cruise vacuum is, not the idle. The power valve won't be in the circuit at idle, unless something is messed up on your carb. I have a motor with 8" idle vac, and cruises at 16. I run a 8.5 PV in it. Even with a 4-speed and normal driving, it doesn't open earlier than I want.
I have never seen a carb with a valve in the rear. Are you certain it is not just a plug? I thought those were for a specific application?

I’ve always gone a few inches less than idling in gear. If that valve opens up at idle it’ll be way too rich.

 

[moparmarks]

I’ve always gone a few inches less than idling in gear. If that valve opens up at idle it’ll be way too rich.

I've always gone half of idle vacuum

 

[65_Satellite]

Your power valve should be determined by what your cruise vacuum is, not the idle. The power valve won't be in the circuit at idle, unless something is messed up on your carb. I have a motor with 8" idle vac, and cruises at 16. I run a 8.5 PV in it. Even with a 4-speed and normal driving, it doesn't open earlier than I want.
I have never seen a carb with a valve in the rear. Are you certain it is not just a plug? I thought those were for a specific application?

It’s def got a second PV. I was gonna order the Holley 750 from Summit but it was a week or so out so they suggested their Summit brand that is built by Holley but branded for them. It’s all Holley parts, only diff is instead of having the side bowls come off, the whole top of the carb comes off. Aside of that, everything is the same and how you tune it is the same. This was the spec card out of the box