I have a holley 750 dp

How far can I go ? I'm at .099 right now . My WOT A/F is 12.5 jetting is 76/90

I'm trying to leave the 90 jet and get to 11.5 A/F .

I want to keep it around 90, because when I add boost , I want to have some jet available if I need to jet up .

Hey Brent I think you told me to go to .120 but I cant remember . Please help . THANKS

 

Anyone ?

I've got my drill out and I'm getting bored .

I just checked back at the old post . Brent said try .125 so thats what I'll try .

Sorry I didnt even think about searching old post .

 

Well , I went with .120

WOT a/f ............. 11.7 but sloooowly got to 12.0 at 6500rpm. Jetting went from 76/94 to 76/90


Is this about max on the PVCR's ?

 

You may want to try slightly smaller high speed bleeds. From what I have seen that should flatten out the afr curve and make it slightly richer.

Troy

 

I have the exact same thing happening to mine right now. I have 80/90 in there and it is @ 11.8 (750, .098 PVCR) but it runs like shit. Brent told me to buy downfeed .150 n&s and run a 75/90 and see what that does.. Do you have the downfeed needle and seat? How does it drive with the bigger PVCR's?


79 sleeper what if you dont have adj air bleeds?

Jeremy

 

Well , I went with 76 / 92 jet . WOT a/f are now between 11.5 and 11.8 93 octaine 24 degrees timing

A/F's seem to be the same on 100 octaine and more timing .( 11.7 30 degrees timing ) :scratch:

Opening the PVCR's seemed to have cured the off idle hesitation it used to have . Its much crisper .

Sorry I dont know what needle and seats are in it . Also ,it doesn't look like the air bleeds are changable. I dont know that much about carbs but they look pressed in .


One other thing . Holley says to pick a power valve that's 1/2 the vaccume at idle in drive . ( example : 11 inches = 5.5 PV )
I read here , that you should use one 2 to 3 inches lower than what it is at idle.

My motor idles in drive at 13 " and I'm using a 6.5 PV . Should I be using a much higher # ?

 

Sounds like we are in the same boat

 

It's pretty easy to remove the stock pressed in bleed, and then drill/tap the hole for a screw in bleed. I think I got my screw in bleeds from Quick Fuel Technology. You can get them pre-drilled to specific sizes, or solid so you can drill them. Here is a pic of my main body:

http://199.86.17.107/pics/bleeds.jpg

Troy

 

Quote:

"Holley says to pick a power valve that's 1/2 the vaccume at idle in drive . ( example : 11 inches = 5.5 PV ) I read here , that you should use one 2 to 3 inches lower than what it is at idle."

I used to work for Holley many years ago in the 70s.

The rule for naturally aspirated engines used to be: 13" of vacuum (in Drive) / 2 = 6.5"
then add 1.5" so 8.0". Holley doesn't offer a 8.0" power valve so go up to a 8.5" valve
rather than stay with the 6.5 valve. The higher the number the sooner that the power
valve will open and make the carb go richer.

The members here are saying (with boost) that by using a valve about 3" lower (a 10.5"
valve) that the carb will be richer much sooner. Nothing wrong with trying the 10.5"
valve first and then seeing how it drives with an air/fuel ratio meter. You may find it is a little too rich at part throttle cruise and if so you can then drop down to the 8.5" valve.

Tom V.

 

Thanks for the info Tom . I'm gonna try that .

Standard or high flow power valves ?

 

High flow will never hurt you on even a stock application but "hole" type PVs have no place in a HP application.

Most PVs are window type these days but some vendors offer even a higher flowing model.

Tom V.