66 427/425 4 barrel secondary

[Ted K.]

At what point does the secondary open up? I cannot get my secondary to open while the car is stationary. I can goose the heck out of the carb from under the hood and there is no movement of the secondary linkage.
I have replaced the secondary diaphragm and checked the vacuum openings to the primary and secondaries. Everything moves freely as it should.
I can't tell if they open when driving the car because the sound of the sidepipes overwhelms the usual droan of the 4 barrels when they are open.
Thanks, Ted

[Michael H.]

Re: 66 427/425 4 barrel secondary

At what point does the secondary open up? I cannot get my secondary to open while the car is stationary. I can goose the heck out of the carb from under the hood and there is no movement of the secondary linkage.
I have replaced the secondary diaphragm and checked the vacuum openings to the primary and secondaries. Everything moves freely as it should.
I can't tell if they open when driving the car because the sound of the sidepipes overwhelms the usual droan of the 4 barrels when they are open.
Thanks, Ted

Ted, testing in the garage, you would probably see the secondary throttle plates open about 3000 or 4000 RPM after the engine explodes. It's actually a slightly delayed action.

To assure that the secondaries are functioning, put a bit of clay on the opening stop of the secondary lever and drive the car. Most likely, you'll find that they operate properly and a depression in the clay.

[Bill I.]

Re: 66 427/425 4 barrel secondary

Hello Ted. You will never get the back 2 barrels to open while the car is sitting. It only happens under load, like running through 2nd & 3rd gears. I Have side pipes also, you will "feel" them opening under load, the car pulls harder. I had the same concerns also, but trust be, if everything is set right, no vac leaks, you'll feel it. Do agree, miss the sound of a Holley sucking 600 cfm. Bill.

[Joe L.]

Re: 66 427/425 4 barrel secondary

At what point does the secondary open up? I cannot get my secondary to open while the car is stationary. I can goose the heck out of the carb from under the hood and there is no movement of the secondary linkage.
I have replaced the secondary diaphragm and checked the vacuum openings to the primary and secondaries. Everything moves freely as it should.
I can't tell if they open when driving the car because the sound of the sidepipes overwhelms the usual droan of the 4 barrels when they are open.
Thanks, Ted

Ted-----


I'll bet there were THOUSANDS of Holley 4 barrel carbs converted to mechanical secondaries because their owners were convinced the "secondaries were not opening" due to a "test" just like yours. I KNOW there was at least ONE "once-upon-a-time" so-converted. It was a STUPID thing to do even for that guy that I KNOW once did it. And, pretty much, it was a stupid thing to do for all the others, too.

[Ted K.]

Re: 66 427/425 4 barrel secondary

Thanks for the comments. I believe it is working as I can feel a little surge kick in around 3500 -4000 rpm wide open, but will try the clay trick to see if it opens up all the way.
Ted