I did not read the entire thread but you can block off all the vacuum lines just for a leak test.

Be sure to always verify the float setting on both bowls before doing any tuning adjustments.

These classic Holley DPs usually run pig rich at idle, so 2 turns out on mix screws seems slightly off. 1.5 is typical if everything is right, so not too far off.

 

First thing that comes to mind is throttle binding. You had the shafts all tore apart, new parts, slow throttle return now.
Using the same return spring? Using the same return spring location or moved it?

I can not think of an extra bolt hole in the Intake that would allow for a vacuum leak. They should all be blind holes.
(Even those bolt holes for vortec heads should not leak air)

Your first priority now if you don't already own one, is a vacuum gauge. Tap into a Full Manifold Vac Port. Only then, can you verify you truly have low vac.

The two-turns-out on the mixture screws is not way-out of specs. I believe about 1 & 1/2 is avg, so your carb is asking for more air.

Not real familiar with your 4776 carb. Your new blades, were they all labeled in the package? Primary / Secondary exactly alike?
Is there a bevel edge on the blade that should only go one direction?

And last, new base gasket under the carb? Quality or budget junk? All four carb nuts / washers (carefully) crisscross snugged down?

 

Sounds like you have some major tuning issues.

• What pistons, heads and C.R. do you have? Stock 9:1 or more like 10?
• That 214* dur cam is pretty mild, but should make a very nice street cam, with good manners. It should make 15" vac or better at idle. What is your idle vac? at what rpm?
• That cam is kind of like a HR version of the 268H, and should build good cylinder pressure, and vacuum, on a 9:1 motor. Those may actually go too high if run on a 10:1 or 11:1 motor.
• 10-12* initial timing is recommended by Barry Grant for small dur cams like that. Bigger cams do require more timing, but not smaller ones.
• But you will also need the vac advance reduced to 10-12* if you want to, and should, run full time manifold vac advance. Factory vac cans give way too much advance, sometimes double that. You should get distributor timing instructions from Lars, and set that stuff first, before doing carb tuning. He also has a 10* VAC limiter you can add. feel free to contact Lars: V8FastCars@msn.com
• That carb is not a good choice for your application, even if new, and will take some serious tuning to get it to run well, and/or be efficient. I would not waste any time on it and just buy a new 650/700/780 vac sec carb, and you will be way ahead tuning wise, and it will run much better. And it would be much easier to tune to your application, and run better. Or a good Q-Jet if you can find one, and have Lars tune that. DP carbs are tuned very rich on the primary side, and run much better on bigger cams like 230-240*, and on your smaller cam will run very very rich due to the increased vacuum. A good tuner, and a lot of work, would be required on this carb, and yours may have been "messed with" a lot, so that makes it even harder, and it could be just ruined.
• If you keep it, be prepared to spend a lot on gas money. Unless you send a lot of time & money with a good tuner.
• Running better or worse by plugging or unplugging your PVC means you air fuel ratio is way out of line.
• That cam should run really crisp, even at low rpm, and thru midrange, up to 5600 rpm, and make good power if you have decent aftermarket alum heads. The timing and the carb are the problems.

 

I disagree with some of the above.
There is nothing wrong with a double pumper on the street. No lag, no delay.
Somebody tried to work on it, swapping the jets front to rear and drilling holes in the throttle blades.
He has installed new blades.

The O.P. has already reduced the primary jets.
Stock primary is 69.
Sec jet is 71.

I would certainly save this carb. It will come around once tuned.
Better than spending $ 600 - $800 on a new one.

This carb has 1.563 throttle blade / bore. Its 600 CFM, a little small, but designed for muscle cars in its era.

 

They all have their place.

Yep. A lot of people like DPs. They can run well. And a lot of people know how to tune them.

But they will rarely give you the mpg of a vac sec, or a Q-Jet. They just don't. DPs almost always seem to burn a lot of fuel.

And Q-Jets are very good, but are also nortoriously difficult to tune.

A Vac sec is kind of in the sweet spot, especially for the street. They tune a lot like a DP, and they almost always burn less gas.


Once your cam goes over 230 or especially 240, a DP is probably easier to tune at that point, and then recommended. This is the application they are intended for.

But smaller cams, like the OPs, will tune in easier and quicker, with a vac sec. The application they are intended for.


The OPs DP can likely be tuned back in, if he is willing to work at it, buy a vac gauge and a an AFR gauge, and go deep into carb tuning, spending a lot of time. Experiment with both jets and air bleeds. Or he could just cover up issues with big accelerator pump squirts, and burn lots of gas, like single digits.

I can tune the richness back out of a DP, but it is a lot of work. It is even harder with smallish cams. You have to practically re-engineer the primary jets and air bleeds settings. It is just easier to put the right application carb on there in the first place. But once the money is spent, I get it. The tradeoff becomes time vs money. And carb money now or gas money later.

See this thread for a recent effort:
https://www.corvetteforum.com/forums...ir-bleeds.html
He is now at a nice lean 15-16 AFR at cruise, at high altitude, so likely mid to high teens on gas mileage, with a crisp throttle, with a DP.
Currently at 8 jet sizes leaner than factory. It was pig-rich before. 4000 ft altitude makes it even harder.
383 with a smallish 224 dur cam, 12" vac at idle, 17" cruising, and a rich running 650 DP with huge AFR swings at different throttle settings. Good thing he has an AFR meter! And knows how to use it!

 

Sorry I should have explained it more. I meant to say that the engine rpm is slow to return to idle. No binding of any kind, throttle returns fast. All four blades were the exact same looking. The kit I got had no instructions whatsoever. The gasket under the carb is a nice one, I have taken the carb off a few times but I doubt that to be the problem. I'm going to look into the blades some more, I must have done something wrong.

 

I'm not sure on the compression ratio, I did not purchase the aluminum heads. The engine builder for this went through them and said they were some type of speedmaster heads, there's no numbering that I could find on them to identify them.

Unfortunately my vacuum gauge broke so I'll need to get another one of those (I dropped it ), but it was running around 14" vac.

My current idle timing is 12*, total of 36. At one point I got this engine running great. Then I messed it up changing the throttle blades, but it did seem to like that a lot.

 

Okay I figured out my secondary adjustment screw was too far, making the secondary's too open. I figured out a way to adjust it without taking the carb off which is nice. But how do I set the secondary's correctly, I've been setting them to an 1/8 turn past where they start to bind, which being that I installed new throttle blades is probably different than stock.

 

Both the primary and secondary should be set to .020" of the transfer slot showing. For first start.
The point where it looks square above the throttle blades.
As a rough first guess, for the secondaries, set the light gap the same front & rear.

You also need to be sure you centered the new blades. IIRC you can do that by looking at the slivers of light sneaking past the blades, they should be even. Both blades should go dark at the same time, or re-center.

Some suggest marking your primary idle screw with a line of white paint at that spot. So you can tell where the slot is with the carb on.
Then adjust the idle speed by opening / closing the secondary blade gap, not the primary. This solves a lot of bog issues. Can sometimes do that with a bent hex key or screwdriver on the car. Basically you do not want to make big changes to the primary .020" opening.

 

The secondary stop screw should be set to have the same "light gap" on the secondary blade bores as the (properly adjusted) primaries do. Hold the carb up to the light after the primary is already adjusted and make the light gap on the secodary butterflies match the light gap on the primaries. You will not have a secondary transfer slot exposed on that carb. The 4776 carb is primary idle only, not 4 corner idle.

Jets should be 66 primary and 73 secondary if you want to get back to stock as built.

 

With a used carb, you should also probably wiggle the throttle/shafts to see if that affects the return to idle. They may be binding, or leaking air.

A throttle shaft leak test would be to spray propane at the throttle shaft to body connection, and see if idle speed goes up.

 

I don't see why the OP secondary would not have a transfer slot.
It's basically just another Holley 4150.
Model 4776, 600 cfm, D.P.

Seems to be a lot of confusion on this carb and internet data about jet sizes.

 

Holley 4150s do have a secondary transition slot, and an idle circuit. It is designed to run all the time. For one it keeps the fuel in the bowl from getting stale. It also helps the idle. And keeps the blades from sticking. But they do not flow as much as the primary, and are not usually adjustable, except on 4 corner idle carbs. Completely shut the secondaries, for a test, if you want, and you will have to change the front mixture screws to get it to idle.

As the secondaries open, more slot is exposed, and the fuel flow increases 4-5X. This covers up the bog that sometimes happens before the secondary main jets kick in. To fix that bog, on a DP, you give it more rear shooter. To fix that bog on a vac sec, requires sec idle air bleed changes, or sec IFR changes. If you have the sec throttle open more than normal, for a big cam etc, you use up the rear T-slot quicker and are more likely to have the bog.

Try to keep both the front T-slots open @ .020" at idle. Especially the front one. .030" max. Or bogs may result.

 

Leigh,
The original poster has a 600 Double Pumper. This is a 650 Double Pumper so it is almost the same as his.

Properly adjusted Primary transfer slot EXPOSED just far enough to look like a "square" between the 2 blue arrows.


Primary transfer slot shown with butterflies open.


Secondary butterflies properly adjusted. Blue arrow is pointing at tiny secodary bleed hole. This bleed is not adjustable.

This picture shows the Secondary butterflies adjusted to have the same "light gap" as the properly adjusted Primary butterflies. Notice that there is no EXPOSED transfer slot on the secondary side. The blue arrow shows a tiny hole that bleeds gas from the secondary bowl during high vacuum conditions. The secondary transfer slot is there but it is not exposed.


Secondary butterflies open to show the secondary transfer slot. On a 2 idle circuit carb such as this, the secondary transfer slot is not exposed at idle. If you can see it, you have the secodary throttle stop screw way out of adjustment and the car will idle very high and/or badly.

 

Excellent pics!
Based on that, this DP may not expose the secondary T-slot.

But your 2 turns out on the idle screws is still a little off. Probably means your front T-slot is off.
Set the front T-slot to .020. Then your idle screws should work better. Set them to 1-1/2. Should be close.
That is extremely important on a Holley for best off idle response.
Adjust the rear blade screw to adjust the air to correct your idle speed. Not the normal idle screw. Just this time. (This is a coarse idle speed adjustment. Use the normal idle speed screw later, but only for minor adjustments.)
If you had to tighten the front to get to .020, you should open the rear the same amount.
It may not expose the sec slot on your carb, but some idle fuel still comes out of that exposed hole.
The carb does not care if the front & rear opening is the same, but it does care if the front slot has .020 exposed.

Your slow return to idle could be caused by nozzle drip, due to the front open too far.

 

Great pictures. I have set the carb up just like you have shown, to a square. Will go and test that out.


I have a lot of confusion when it comes to the .020 gap. I have a picture below showing a .020" gauge in the throttle bore, it exposes a lot of the transfer slot. I must be doing something wrong.



Also I doubt this is very important, but I wanted to know why this hole only exists on the one side for the primaries.

 

That's not how to feeler gauge the transfer slot. Your photo would be measuring how far the blade is open. Not important.
Place the feeler gauge where it can measure the slot height, not blade opening.
A square "looking" slot will be 0.020.

 

I think the red arrow is the source of your ported vacuum. Barb fitting is probably the one right behind it.

 

The feeler gauge picture you posted is not the way to do it. The primary "square" is right. On the secondary side you will not see any "square". You will hold the carb up to the light, look at the amount of light that passes through between the primary butterfly and the primary throttle bore. Hold it just right to see the "moon" shape. Duplicate the "moon" shaped gap on the secondary side butterflies using the tiny secondary stop screw. This screw is only accessible from the underside of the carb.

It's very tricky to change the secondary stop screw with the carb installed, and there is no way to "measure" it once installed. You need to get it right before installing the carb.

 

I have taken the carb off a million times today. I'm struggling to see a relationship between the secondary's. I have been turning them an 1/8 of a turn at a time until they were each a +/-1/2 a turn away from stock. I've finally got it to idle good. But it just seems wrong to me. The secondary's are very close to shut basically a quarter turn away from binding shut, and the idle fuel adjustment screws are about 3 turns out each. Engine runs very smooth at idle. But it's just weird to me how it is working. I have yet to check for throttle shaft leaks, but I should do that. I'm unsure of the primary position, but they are probably close to 0.030-0.040 open to keep the idle up.

Yes at this point I should probably just get a new carb. But at the same time it feels like this carb can work, I'm just not understanding it.