Another carb question

[1972orangebeast]

ok guys been having trouble getting my combo to run well. I have 3 different carbs lying around and just can't seem to be the right combo together.

My setup is a stock 1976 RV 360bottom end, Eddie rpm heads, lunati voodoo 226/234 @.050 lift 494/513, rpm air gap intake, stock electronic ignition with a jegs adjustable distributor, 16/17* initial and 34/35* all in around 2500

I have a Holley r47774 650dp mech sec jets 67/73 squirt 28/28 and 6.5pv, this ran ok but was lean, just didn't quite rev quick or pulled very hard compared to 750s

Next is a Holley 3752(can't seem to find out exactly what this carb is) best guess 750dp , jets 68/76 sqrt 28/31 6.5pv, ran the best but is super rich at idle and plugs are black.

Last is a speed demon 750, jets 76/83, Sqrt 31/31, 6.5pv, ran ok but rich, leaned jets up to 72/79 damn thing would barely idle and kept back firing.

Any suggestions would be great! I think my next step is to take the Holley 760 and lean it out by 2 jet sizes.

 

[brian6pac]

The main jets are for WOT not idle. Don't change them for a idle problem.
1. How much vacuum at a idle
2. How far are the throttle plates open at idle, if the throttles plates are open
to far you will be off the idle circuit. If the pv is old they get stiff and don't move and cause a lean condition off idle.

 

[1972orangebeast]

Ok with the Holley 750 dp at idle with idle screws 1 1/2 it idle between 8-10 vac if I turned them in 1/2 it jump up to 10-12 still very rich. The Holley already has holes drilled in the main butterflies, and has 4 corner idle screws. Here's a picture

 

[brian6pac]

pv should be half of your idle vacuum, 10 in 5.0 pv, 8 in 4.0 pv or 3.5

 

[AJ/FormS]

Re-read Brians posts

I had a combo just about the same as yours,with a 223/230 cam, and 10.9 C/R. It ran gangbusters with a 750 dp. 600 was waaaay too small.
My current cam is a 230/237, and still with 10.9Scr.I run 72/78s with a 8.5PV. It is a stick car.
Neither of theses cams needed much Idle-Air Bypass, and I run just 14* initial. The all-in I have set to 32/34 at 3400 so I can run 87E10 on 10.9Scr.
The secret is to get the T-port synced up to run 3/4 to 1 turn on the mixture screws, and with the float level stable and slightly low in the primary bowl.
It sounds like you are pretty close.
At idle,
it does not matter what size main-jets are in there or even if there are none at all. In fact the slow speed system will work just fine to about 30 or more mph,if you never opened the throttle more than to about the top of the T-slots.
Those transfers are your slow-speed fuel-delivery system. The mixture screws are enrichment for the idle. The fuel level is almost critical for this circuit to function correctly.The PV HAS to be 100% functioning correctly.It is possible for fuel to pass through a ruptured diaphragm straight into the intake, and you would never see it at the boosters.So put a plug in there and tune the idle with out it. That is what I do, I get rid of that variable.
I'm thinking your PV is ruptured,or the fuel level is too high or unstable, OR your idle-air bleeds are not working right; have you blown them out?
The valves have to not be too tightly lashed.
>The main jets are scheduled to start flowing as the Transfers are maxing out, and when the right size ones are in there, they will be maxed out at about the time the manifold vacuum has dropped to about 10", while in gear and accelerating. At that time, the PV should begin to flow.
>I run as small a MJ as possible for fuel economy, and get the PV opening as early as possible,to cover the hole the lean MJ might cause. I try to tune the primaries a hair lean with the secondaries disabled. And I run a 10.97 starter gear to get me thru any low-speed glitches.You won't believe how much torque/power the 750 can make on primaries alone. I think it's good to about 25/30 mph in my combo.
And don't underestimate the power of the vacuum advance system. I run 22/24* and bring it in really fast; those aluminum heads just eat it up.I'd run more but that is all I could get,out of mine.