'65 396 3124 Carburetor Questions

[Tim Genovese]

What function does the vacuum hose that runs from the exhaust manifold to the secondaries perform?

How do I increase the fuel level in the secondary bowl?

Before you say to order the shop manual...I ordered it this week from NCRS.

[Joe L.]

Re: '65 396 3124 Carburetor Questions

Tim----

The hose that goes from the carburetor to exhaust manifold on the right side of the engine is for the carburetor choke heat. It is not a vacuum line at all. Later year model big blocks don't use this system since, starting in 1966, GM went to manifold crossover mounted choke stoves.

As far as adjusting the floats goes, as far as I know, all Holley carburetors adjust floats in essentially the same manner. Each float bowl has a locking screw and a float adjusting nut beneath it. To adjust float level, one loosens the locking screw and turns the adjusting nut to raise or lower float level. I realize that 65-396 cars with the 3124 carburetor use uniquely configured fuel bowls, but as far as I know, the adjustment methodology is the same.

[Tim Genovese]

Joe -- Re: '65 396 3124 Carburetor Questions

There is a choke line but also a second line the enters the bottom of the exhaust manifold and runs into the top of the carburetor on the secondary side of the carburetor (passenger side).

I have assumed that this line is a vacuum line because vacuum is present but I don't know its function.

[Joe L.]

Re: Joe -- Re: '65 396 3124 Carburetor Questions

Tim---

You know, now that you mention it, I do recall the other line. As I recall, there is a small diameter rubber tube which connects, at the top, to a metal tube which angles out from the top of the carb air horn. The rubber tube then extends down the right side of the engine where it connects to a metal tube which, in turn, connects to, as I recall, the exhaust manifold just above the heat riser. But, you know what? You've stumped me. I used to know what this was for but I've forgotten! That's what happens as you get older.

Anyway, there must be some 396 experts out there. Refresh my memory. Now you've got me curious.

[Tim Genovese]

Re: Joe -- Re: '65 396 3124 Carburetor Questions

I'm asking the question because I'm trying to figure out why my secondaries do not work.

[Page C.]

Re: Joe -- Re: '65 396 3124 Carburetor Questions

Hi Joe I believe this is the source for clean air ( air that has been filtered thru the air cleaner) prior to going thru the exhaust manifold on the way to the choke. This was designed to keep dirt and trash from being suck into the choke when the engine was cold . The NCRS Restore Vol.25 #1 has a great article by Gary Hodges that shows this setup on a small block. Page Camprbell#2299

[MikeHom]

Re: Joe -- Re: '65 396 3124 Carburetor Questions

What leads you top believe that the secondarues are not working?

[Robert P.]

Re: '65 396 3124 Carburetor Questions

Tim, I've been watching this tread with interest for a few days. The answer from Joe and others are very accurate...

IMO, there is no connections to why the "secondaries" are not working. However on the lighter side, if you could get the car to me here in Virginia, I'd love to take it out for some "deep breathing" excerices in an attempt at determining why they aren't working.

I doubt that will come to past, so here's the scoop (or my take) on the lines you are referring too..... I'm sure its similiar to my '65 327/350 - 2818 carb. The steel line that connects the choke hsg to the exhaust manifold draws heat from the ex manifold thru the base of the carb (inside the choke housing is a piston type valve). I don't know the physics of it, but someway / somehow it draws a vacumm thru the base of the carb. The other tube is simply a vent that connects to the top of the carb and enters the bottom of the ex manifold. They both connect to a hollow tube inside the ex manifold that is heated by the engine exhaust and as a result the heat opens the choke.

BTW, I implemented a method that is not NCRS approved to overcome the same problem with mine and a friends '66 in 1966. I'm sure many that grew up in that era no exactly what I'm referring too.

Other comments / suggestions welcomed.

Bob

[Joe L.]

Re: '65 396 3124 Carburetor Questions

Bob----

If you're talking about that little "problem" with vacuum secondaries "not opening", I think I came up with the same "fix" back in 1966 for my Chevelle SS396. In fact, if I remember right, there was this cheap little kit that I got at my local speed shop.................This Forum is dedicated to restoration, though, so I won't go into it, either.

[Tom Buddie]

Secondary Test

This is the only accurate way I know of to REALLY determine if/when the secondaries are opening when they're supposed to: Rig up a micro-switch to the bottom of the vaccum rod which activates the secondaries. I use sheet metal to fabricate a bracket to mount the switch on the carb mounting stud. The switch I use is a "NC" normally closed single pole, single throw. This means when it is at rest (non-toggled), it will have continuity. Mount the switch so that it is contacting the vaccum rod, and the switch lever is depressed when the secondaries are supposed to be closed (engine off). When the vaccum rod moves to open the secondaries, the switch lever will move "up" to its NC normally closed position. The switch can provide a path to ground (-) for a 12 volt bulb (or anything else) to signal that the secondaries are opening. I used this method many, many times to troubleshoot both 4 bbl and Tripower setups where the secondaries were not opening. It may be "Hokey" but it works great for me. I've been doing this since 1969. Just make sure you look over your shoulder when you're stomping on the throttle.