Secondaries sticking

[Warriorautotech]

Hi all, im new here but ive always been a fan of the quadrajet. I run a dodge dakota pure stock on dirt and im having some odd isues with the secondary air doors. My engine is a 360 magnum with 89-92 308 tbi heads, factory dodge quadrajet intake and magnum 2.25 outlet exhaust manifolds, 68 340 manual cam, 221/227 duration at .050, .438/455 lift on 114 degree lsa. 1" 4 hole phenolic spacer under the carb and a 5" aluminum spacer between the carb and air cleaner. The carb is a mid 80s dodge heavy duty truck carb that ive worked over following ruggles recipe 2 in the book. The issue im having is that in mid turn when i start getting back on the throttle most of the time the secondaries wont open, from a dead stop they work better. The problem got a lot worse after i swapped to this current cam from a much smaller one. I have a front mounted sec vacuum pulloff comnected to b port above fuel.inlet. my theory is that the spacers create a high velocity venturi effect under the primaries which is not allowing the vacuum to drop below the primaries so the pulloff can release at 4500 rpm part throttle .i know that the engine runs much richer without the 5 inch spacer.  Im switching to a rearmounted pulloff connected to the rear vac port that pulls from under the secondaries which hopefully will fix this but i wanted some opinions from others. There are no binding issues at all in either the secondary throttle plates or air doors.
 The other issue im having is since cam swap i cant get enough fuel when secondaries do open, i have .041 rods and a b hanger at the moment with .036 secondary air tubes and my afrs are still around 15:1. Can i switch the secondary air bleed tubes to richen it up? I have a set of .025 tubes out of a  feedback carb i can use, but every recipe in cliffs book calls for .036. Thanks for any input

[Warriorautotech]

I dont know why it cut my post off. Ill try again
Apparantly the forum computer doesnt like the degree symbol

[Warriorautotech]

ill add that float level is at 1/4 and fuel pressure is a steady 6 psi at wot, holley racing mechanical pump and holley fuel pressure regulator

[Warriorautotech]

no one has any input?

[Mudsport96]

Just a guess, but you could run hose to a port on the manifold and see if that allows the secondary side to open. Also if the choke is not fully open it can lock out the secondaries

[77cruiser]

The vacuum will hold them shut & it overrides the spring. Read where some stock class & SS racers drill the arm & shaft & put in a roll pin.

[Cliff Ruggles]

Carburetors can be sensitive to air cleaners, air cleaner lids, velocity stacks and other items mounted above them.

They can also be sensitive to spacers used under them.

I've tested gobs of spacers, and air cleaner assemblies over the years, and remarkable find that the vast majority of them hurt power and engine performance vs helping it.

Case in point, at the track on back to back runs I tested four different 1" spacers and no spacer at all.  My engine is a LOT more powerful than your 360, making up near 600hp and over 600ft lbs torque.  The intake used is a CNC ported factory unit, with the divider in place but small "notch" out between the secondaries.

Here's what I found.

It ran worst with a 1" thick four holes spacer and with a 1" thick fully open spacer.  The fully open spacer actually induces a slight stumble/hesitation/bog going quickly to full throttle that was difficult to tune out.

It ran well with a 1" fully divided spacer and better with a 1" semi-open spacer (notch between the secondaries).

With the semi-open spacer the car picked up nearly 1MPH on top end. 

Even with some additional top end charge when the smoke cleared and dust settled the quickest ET was attained mounting the carb directly to the intake with a 1/4" thick fully open gasket....go figure?

So even when we add parts that make more upper mid-range/top end power, losses at lower RPM's or loss of average power may not achieve improved vehicle performance.

I found similar results with things added on top of the carburetor.  I tested several air cleaner assemblies, and nothing at all above the carburetor.  For all testing I still pulled all the air thru the Shaker assembly.

continued.....

[Cliff Ruggles]

I even tested the K & N X-Treme lid.  Once again, when the smoke cleared and dust settled the factory air cleaner lid with a stock height air cleaner element ran the best for ET and MPH.  So there is something to be said for directing the air into the carburetor as the factory lid is very well made with a nice raised area to it and gentle turn to direct air into the carburetor.

Not sure if any of this helps or not, but I have found that messing around with spacers and things added above the carb to improve airflow can disrupt airflow, cause hesitation, stumble, bog and slightly losses of power enough to offset any advantages to them.

You also have to realize that dirt track racing, like drag racing is not a static environment.  There is a LOT going on with fuel delivery and fuel control in the bowl of the carburetor.

When I build racing carburetors here, fuel control and venting are high on the priority list to keep the jets covered and fuel in the bowl on hard runs. 

Some Q-jets, especially the later model ones have a LOT of places for fuel to "slosh" out of the bowl in a dynamic scenario. 

Might want to take steps to control the fuel, and maybe look at some of the results listed above with help to cure the issues.

If you can't get enough fuel to the engine with .041" secondary metering rods the problem may be elsewhere and not related to how the carb is set-up.  Some parts create turbulence, like using open spacers on dual plane intakes, or grinding out the factory divider, for example.

Right on the dyno we gained 60ft lbs torque putting a divider back in a very well prepared custom ported factory intake for a "stock" racing application.  Yes, even though the custom ported intake with fully removed divider made a couple more HP on top end, mid-range power was down 40-60 ft lbs torque in the mid-range!

So when modifying intakes and air cleaner assemblies, testing spacers and air induction systems, look for best average power (torque) for best vehicle performance vs making a few more HP on top end and having power suffer elsewhere in the RPM range.

As far as "sticking" secondaries the choke pull-off plays a role in smooth transition with the air flaps.  It should never be removed like we see lots of folks doing for dirt track racing as this requires the spring to be would too tight to prevent a momentary lean condition when the flaps "whip" open too quickly.

With a "timed" pull-off, when only provides a momentary dampening effect but smooth opening rate we can set the spring tension on the flaps much lighter.

In ALL scenarios going to heavy/full throttle vacuum to the pull-off is near zero or low enough it will not prevent or hinder the opening of the secondary flaps.........Cliff

[Warriorautotech]

Thank you for the input, i ran the tall spacer on top to get the aircleaner above the dakotas hoodline for cooler air, i will try without it though and see how it runs, im also going to pin the secondary shaft to the lever to force them open at full throttle. Im only concerned with max power between 4500 and 6500 rpms, so torque numbers below that are less important to me. What about the .025 secondary air bleeds? I went ahead and put them in and running the truck in the air while dragging the brakes my afrs were a lot better, around 12.5 consistently. Will the smaller air bleeds cause any other problems? Btw i have blocked off the secondary vent and pullover vent holes, i vented the pullover wells internally to the float bowl, i also taped over the secondary rod holes in the gasket.  The only vent i have on top is the round pipe and ive extended it about 2 inches. My fuel delivery is fine, i have a mechanical fuel pressure gauge on the dash , 6 psi never drops. and im running about 35 degrees of timing if that matters. I need to keep the left and right bank seperated to keep my vacuum up above 16" to be legal, right now im at about 16.5" hot at 1k rpms

[Cliff Ruggles]

Tuning for upper mid-range and top end power is fine, but you still have to avoid parts that can cause transition issues on and off the throttle.  This will include mods done above the carb and certain spacers.

Case in point.  We build carbs and help folks set-up combinations for FAST Class drag racing.  One of my customers and good friends hired out his intake to be professionally ported (factory cast iron).  They did an EXCELLENT job on it, but removed the entire divider between the plenum areas.

On the dyno he picked up some HP right up near the shift point, but it KILLED off mid-range power and the engine developed a "stumble" anytime he went to full throttle.  We "notched" the intake and installed a custom made aluminum divider plate, the stumble went away, and the car was a LOT quicker at the track despite the slight power loss at really high RPM's.

So average power w/o transition issues still trumps a little more power at really high RPM's........Cliff