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The secondaries are almost closed. I cracked them open about 1/3 of a turn on the screw.
Good. That means it's "about right" as far as all that goes.
Dart_68, A lot of things are not adding up..... Only 5" of idle vacuum, & you want it to idle at 700 rpm? I doubt that will happen. If the low vacuum is from a long duration cam, hard to believe that both pri & sec t/blades are almost closed, because the engine should need a lot of bypass air for it to idle. The engine gets this air from opening the t/blades further, drilling t/blades, etc. Do you know the cam specs & comp ratio?
Mine only idles at 6" with 250@.050 on a 108. It WILL idle "around" 750, but it doesn't like it. It'll stall every once in a while coming to a stop. If I idle it right up around 1000, it likes that much better and never stalls. At that idle speed, my primary t slots are BARELY larger than square and I can close the secondaries all the way down until they stick shut. I have them adjusted now so they just barely will not stick.
I wonder if the PCV [ if used] is part of the problem. Probably open at idle, admitting a lot of air, hence t/blades not reqd to be cranked open further.
Sounds like it's getting air from somewhere if closing the air screws won't kill it, doesn't it?
Problem? The word "Holley" explains said problem.
I've replaced the current PV with a 25 (was 65). Secondary throttle blades were 2 turns out from fully seated. I set them to 1 turn for startup. Idle mixture screws set to 1 1/2 turns out for startup. Primaries set with a "square" of the transfer slot showing (picture). I've not had time to start it since I set changes back to what I believe is square 1 but I'll keep you up to date when I do.
What is the idle vacuum reading warmed up and in drive?
Nevermind. I forgot. You already said 5". The PV makes ZERO difference at idle. There is nowhere for the fuel to go if it's blown or open. The boosters have to have a signal to pull fuel into the venturis and without the throttle open, that ain't happenin. Effectively, you could throw the PV in the ditch and tune correctly for idle.....so don't get caught up worrying about the PV "right now". That said, you are at a good starting point for the PV now though.
Crap, what's the duration @.050"?
Here are the cam specs as provided by Oregon Cam Grinding. Cam lobe lift .359 intake .372 exhaust Duration @ .050 - 235/247 Lobe separation 110 Intake center line - 106
You got somethin WRONG. There's no way in HELL that cam is not pullin more vacuum than it is. Maybe a wrong gasket in the carburetor....internal vacuum leak or somethin.....Hell, my slant 6 pulls more idle vacuum and it has 250@.050 on a 108. Let's go the direction Bewy was.....are you running a PCV valve? If so, yank it off and plug the port where it's plugged in....and that IS in the carburetor, right?
PVC is connected to the throttle plate port on the back of the carb and gets full manifold vacuum.
As an FYI, I've looked for vacuum leaks elsewhere and can find none. No uncapped or unused ports, no leaks around the base of the carb or intake. Only place I can't look is the underside of the manifold.
It CAN idle at 700...it just doesn't like it. 850 is far more stable.
Find someone with a known good carb you can test your Holley against? Lol, can't or don't want to. (Just kidding) Could you possibly be pulling air from an internal heat crossover leak?
Well, the intake is a Holley Street Dominator so there is no heat crossover passage. However, it does have an EGR mounting pad but I've checked that for leaks.
If it’s a STREET Dominator it has a heat crossover. If it’s a STRIP Dominator it doesn’t have the crossover.
Perhaps you're correct but the heads are Speedmasters and they don't have a heat crossover.
Can we get a list or model number? How much adjustability does the carburetor have? Air bleeds? Fuel restrictors? What exactly are we talking about in a carburetor here?
Its a 3310-2 VS 750 CFM. Air bleeds are not adjustable. Only things you can readily adjust are idle fuel mixture via the screws, main fuel mixture via standard jets and PV, secondary main metering via a plate, primary and secondary throttle blade positions, float level, and VS opening rate via a diaphragm spring.
It sounds like you need to lean out the idle circuit. Only way to do that I know of is to modify your existing metering block, or get one that has replaceable fuel restrictors. I guess you could do the age old trick of drilling small holes in the primary blades, but that's drastic, IMO. Plenty of folks have done it with good results.
So, is this a new carb, old carb, rebuilt, has it ever had proper idle screw operation?