Secondary’s on edelbrock 600cfm carb not opening

[Hayden’s72]

I have a 1972 c20 with a sb350. The carb is a 600cfm edelbrock 4barrel. I have noticed that it doesn’t kick down a gear when gunning it and doesn’t have that “feel” that the secondaries are opening. So sure enough I opened her up and looked into the carb and they are not opening. Have any of you had this prob? How can I fix it? Thanks.

[demian5]

Sounds like your kickdown cable isn't adjusted properly. Post a picture of the cable setup and a picture of the carb from the top as well, then we know what you are dealing with and can help..

[Hayden’s72]

Here are some pics

[Steeveedee]

Looks you have a secondary air valve in your carburetor. If so, cranking the throttle open won't show the secondaries opening up, because there is no vacuum pulling the secondary air valve open if the engine isn't running. With the throttle held wide open, use a pencil or some other poking device to open the air valve. Then you will see if the secondaries are opening.

[gvw5400]

One thing to check is the choke adjustment. When the engine is warmed up does the chokestat open the choke plate all the way? If not the secondaries will be lock out.
Also check that the transmission downshift cable pulls all the way forward at wide open throttle. Also welcome to the site!!
All the best,
Dirk

[Metaldoc]

Make sure the butterflies are not hitting a gasket, just got a new carb with that issue.

[demian5]

Originally Posted by Steeveedee

Looks you have a secondary air valve in your carburetor. If so, cranking the throttle open won't show the secondaries opening up, because there is no vacuum pulling the secondary air valve open if the engine isn't running. With the throttle held wide open, use a pencil or some other poking device to open the air valve. Then you will see if the secondaries are opening.

He has the tons-o-fun weighted secondaries. I'm battling the secondary opening of those as well. But I know mine are working.

That vacuum line for your vacuum modulator looks almost falling off the nipple on the intake.

Make sure the choke is open. You shouldn't need to see down the hole to verify the secondaries are opening, just watch your linkage. How about a picture of where the kickdown cable is attached to the bracket so we know what kind of adjustment you have?

And try and get the pictures oriented right by doing a test post before actually posting.

[demian5]

And this shows how to adjust the kickdown cable. Best one with images of the tab I have seen.
http://forum.73-87chevytrucks.com/sm...?topic=31453.0

[stsalvage]

I found out something with my 1972 3/4 ton 350 with the th350.The Vacuum modulator on the back of the trans is not adjusted right or the governor is set to tight.That can cause a lot of no kick down my 2 speed power glide shifted harder then any of the GM transmissions mine was all linkage no cables No lag

[RichardJ]

Any transmission problem would be a separate issue.
The Air Valves that you can see looking down into the carb are not connected to linkage or anything else. That assembly with the counterweights on both ends just lays in there above the secondary throttle blades. They open by airflow not vacuum. They open gradually as air flow and rpm increases. Without these valves, the engine would fall on its face at lower rpm when you stabbed the throttle. WHEN DRIVING.

The Edelbrock AVS, Air Valve Secondary. has the valve mounted higher, in the air horn and has adjustable spring tension instead of weights.

[davepl]

I think it's covered above, but to be pedantic about it, that's not a "mechanical secondary" carb so they will not open by operating the carb linkage.

They operate from a vacuum diaphragm that is energized by air flowing throw the carb primaries. The more through the primaries, the more the secondaries will open. So you can't just check it easily on a bench like that.

Remember also that even on the car they will not open until there is a demand, and your primaries can likely feed the first 275hp of power, so they may not open at all until higher RPM at full throttle anyway.

[demian5]

Originally Posted by davepl

I think it's covered above, but to be pedantic about it, that's not a "mechanical secondary" carb so they will not open by operating the carb linkage.

The secondary butterflies open (mechanically through the linkage) and the vacuum created by them opening, pull the butterflies open. The weights are in place of the spring and cause resistance to the vacuum pull, to assist with a smooth transition.