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Too lean at wot?

Jonas Nordstrom

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Im a bit puzzled here about the next step to tune my carb to get richer at wot?
Right now when going flat out I am around 13.8-14.2 in afr.

Classic Holley 650 VS.
63 jet in the primary and 73 secondary.
7.5 power valve. (Idle in gear auto gives 16hg.)
Timing (14 BTC) and floats adjusted.
Cruise afr: 13.8
Ive checked that the secondaries opens all the way(zip tie.).

I feel Im at the limit of distance between jets, but shouldnt wot afr be around 12 to be healthy?

Thanks in advance.
 
No rules that I know of about the difference between primary and secondary jets.
Do what the engine needs.
From your post jump up 2 jets sizes on the secondary jets.
12.5 - 13 for most engines.
 
I have read articles about "supposed" to be 8 jet sizes difference between primary and secondary as well. Don't think I have ever ended up more than a 10 size difference, and you have a ways to go yet. Another big contributing factor to WOT A/F is the size of your PVFR's. You tune them in conjunction with the secondary jets at WOT. I always shoot for 12.2 - 12.4 at WOT. What size motor are you dealing with?
 
I have read articles about "supposed" to be 8 jet sizes difference between primary and secondary as well. Don't think I have ever ended up more than a 10 size difference, and you have a ways to go yet. Another big contributing factor to WOT A/F is the size of your PVFR's. You tune them in conjunction with the secondary jets at WOT. I always shoot for 12.2 - 12.4 at WOT. What size motor are you dealing with?

Ok, will test that. I have tested some and know that even a 9.5 PV worked fine on my engine (Though never tested that high PV with the current jets.).
Its a mild 413 that gives 20Hg at idle park.
 
Ok, will test that. I have tested some and know that even a 9.5 PV worked fine on my engine (Though never tested that high PV with the current jets.).
Its a mild 413 that gives 20Hg at idle park.
I'm not talking about the power valve itself. When you unscrew it, there are 2 small jets drilled in the housing at an angle, called the power valve feed restrictors. These are what you use to keep a nice cruise A/F mixture, but richen things up when the power valve opens, and are very important. So when you floor it, you are using the primary jets, PVFR's, and the secondary jets. All 3 contribute to WOT A/F.
 
Also, what is your cruise vacuum? I bet you could go up to a 12.5 power valve.
 
I'm not talking about the power valve itself. When you unscrew it, there are 2 small jets drilled in the housing at an angle, called the power valve feed restrictors. These are what you use to keep a nice cruise A/F mixture, but richen things up when the power valve opens, and are very important. So when you floor it, you are using the primary jets, PVFR's, and the secondary jets. All 3 contribute to WOT A/F.

Ah, then my guess was right, then I need to get a new metering block with adjustable pvfrs (If I dont want to drill). I guess its time to step up. :)
It was a bit hard to read but my cruise vacuum seemed to be at 12-13.
Biggest I have is a 10.5, could try and put that in.
 
Ah, then my guess was right, then I need to get a new metering block with adjustable pvfrs (If I dont want to drill). I guess its time to step up. :)
It was a bit hard to read but my cruise vacuum seemed to be at 12-13.
Biggest I have is a 10.5, could try and put that in.
If you only have 13" at cruise, leave the valve in that you have. You should have more vac at cruise than at idle though. Sorry about the confusion about the feed restrictors. All my Quick Fuel carbs have replaceable restrictors as did the last couple of Holley's that I had. Didn't even register in my mind that you didn't have that feature.
 
If you only have 13" at cruise, leave the valve in that you have. You should have more vac at cruise than at idle though. Sorry about the confusion about the feed restrictors. All my Quick Fuel carbs have replaceable restrictors as did the last couple of Holley's that I had. Didn't even register in my mind that you didn't have that feature.

It did fluctuate a lot on the vacuum meter when i was trying to get my cruise vacuum (Narrow old road.) so i think I need to get out again to get a proper reading. :thumbsup:
Whats the proper pace to read cruise vacuum, steady drive at 2000 rpm?

No problem, I did suspect that the feed restrictors was the next step.
I wanted to tune the classic Holley as good as i could before I start with my plan to build my own carb this winter.
 
Whats the proper pace to read cruise vacuum, steady drive at 2000 rpm?
Yes, 2-2500 rpm. While you are doing that, watch when your power valve opens as you slowly push the pedal down. That will tell you if you can install a higher number PV.
 
Yes, 2-2500 rpm. While you are doing that, watch when your power valve opens as you slowly push the pedal down. That will tell you if you can install a higher number PV.

Thanks. Will do.
Do I want the Power valve to open as close as possible to cruise vacuum?
When I had the 9.5 PV in I could feel a small nudge in acceleration when it opened, though i dont know if that is correct. (If in reality it was actually a hesitation?)
Now with a 7.5 PV I cannot feel the nudge but have a strong smooth accelaration.
 
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Thanks. Will do.
Do I want the Power valve to open as close as possible to cruise vacuum?
No, you really don't want it to open under normal driving conditions. Just a waste of gas.
 
Just drill the PVCR. Simple, easy, effective.
 
Just drill the PVCR. Simple, easy, effective.
YES.....simple, easy, and effective.....BUT...unless you have a metering block with replaceable Power Valve Channel Restrictions or PVCR's, there is no fall back position if drilled too large, as you sre drilling the metering block, made from a zinc die cast alloy, that will be damaged, if heated to use solder to close the hole. Perhaps a Proformax metering block with REPLACEABLE PVCRs and emulsion channels air bleeds. Just something to consider. IMO....just go bigger on the secondary metering jets as suggested....why....its easier and more effective. If drilling....you must compute the effective AREA DIFFERENCES, not just the diameter differences to accurately determine the additional ammount of fuel flow.
BOB RENTON
 
YES.....simple, easy, and effective.....BUT...unless you have a metering block with replaceable Power Valve Channel Restrictions or PVCR's, there is no fall back position if drilled too large, as you sre drilling the metering block, made from a zinc die cast alloy, that will be damaged, if heated to use solder to close the hole. Perhaps a Proformax metering block with REPLACEABLE PVCRs and emulsion channels air bleeds. Just something to consider. IMO....just go bigger on the secondary metering jets as suggested....why....its easier and more effective. If drilling....you must compute the effective AREA DIFFERENCES, not just the diameter differences to accurately determine the additional ammount of fuel flow.
BOB RENTON
Exactly why I buy carbs with screw in PVFR jets. So easy to fine tune, plus I like experimenting.
 
I would not drill the PV restriction because it may go really rich when the power valve opens and then go leaner as the engine starts to rev up.
If this happens nothing you can do about it. The engine will accelerate faster is it is leaner or correct - if you go too rich it will have to get over the fuel dumping in.
The simplest thing to try is go up on secondary jetting and see what happens.
On a mild engine it will probably be fine.
 
Just go up in the secondaries and see what happens. Don't make it more complicated than it needs to be.
 
YES.....simple, easy, and effective.....BUT...unless you have a metering block with replaceable Power Valve Channel Restrictions or PVCR's, there is no fall back position if drilled too large, as you sre drilling the metering block, made from a zinc die cast alloy, that will be damaged, if heated to use solder to close the hole. Perhaps a Proformax metering block with REPLACEABLE PVCRs and emulsion channels air bleeds. Just something to consider. IMO....just go bigger on the secondary metering jets as suggested....why....its easier and more effective. If drilling....you must compute the effective AREA DIFFERENCES, not just the diameter differences to accurately determine the additional ammount of fuel flow.
BOB RENTON

I suggest not drilling it too large.
 
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