OK -- I got the vacuum leaks fixed and now on to the next issue....

Again - 1982 Z28 with 305 4bbl and 3,100 original miles.

I got the engine running well, check engine light is off (vacuum leaks fixed).

Now, when I "floor" the accelerator nothing happens - the care just bogs down and does not downshift or do anything - the secondaries just don't seem to open.

The car runs great otherwise and gets up to 80+ mph in a steady acceleration, just don't ask the secondaries to open up and help.

 

EVERYBODY seems to think that.

More likely, they're opening TOO much, TOO quickly. Probably MUCH TOO loose.

Start by setting the tension on the air valve spring to about ¾ turn.

Kickdown is a separate matter. Start here. www.tvmadeez.com Read and UNDERSTAND FULLY the "TV 101 Article". All however many pages.

 

Along with the spring tension, the vacuum-operated choke pull-off (GM calls it the "choke break") plays a part in keeping the secondary air valves closed until needed. If the diaphragm leaks, it won't hold vacuum and bleed off like it's supposed to and will allow the air valves to open too quickly.

 

Just to clarify the common "secondaries not opening" mistake - both Sofa and Five7 are spot on.

When you apply throttle cable tension to the carb you open the primary butterflies initially, the more tension that is applied, pushes the rod towards the secondary butterflies further until it makes contact with the bendable contact (adjustable with pliers) and opens the secondary butterflies - that whole process is mechanical - not vacuum related.

What you are referring to is the air door operation. You can have the secondary butterflies open mechanically all you want, but until there is enough vacuum available with the secondary butterflies open, it wont pull the doors down, the metering rod hanger wont lift the metering rods and the fuel will not pour through and be atomised and burned - therefore wont create any more power or vacuum.

you might have a couple of issues

Five7 pointed out the easiest one - and the easiest to bypass - you can remove the stupid rod (temporarily) going from the vacuum cylinder to the secondary air door and also the little key piece that prevents the secondary butterfly shaft from opening fully to test it out.

Sofa pointed out the second easiest yet one of the more frustrating tasks - tensioning the air door. in my opinion this should ideally be done after you have put a kit through the carb plus a couple of key replacement parts

1. Air door tension spring - its been 35 years - you can set it but youll probably find yourself doing it again over time. I've had a couple lose the tension, then eventually they break. Dont get me wrong, if you get one of these things out you will be amazed that something so frail and cheap looking can last for several decades.

2. Secondary air door cam - this little piece of plastic has left many a holden fan (the australian chev) scratching their head because they cant make any power. when those air doors open (in your case they might not) there is a tiny plastic kidney bean shaped cam that pushes the secondary rod hanger upwards and therefore lifts the metering rods which drop fuel into the secondaries. This thing breaks/wears out/mysteriously vanishes over time. Theyre a pain to replace but worth doing if youre gonna put a kit through it.

start with disconnecting the silly choke rod & keypiece dealio

before you play with the air door tension, press down onto the air door to open it manually and look to see if the secondary rod hanger raises up

if it does - move onto sofa's door tensioning.
if it doesnt - rebuild.


another option is to see if you can extend the rod that mechanically opens the rear butterflies when flooring it. - this is done with some careful bending of the rod and the contact point so leave that to a last resort.

 

Th secondary air door not opening isn't going to cause a bog on acceleration. It will just be like accelerating a 2 barrel carb. The bog is more likely the air door opening to easily without enough fuel to go with all that air. Check the secondary metering rods to be sure they are lifting when the air door opens. What five7kid mentioned about the air opening rate and the vacuum break that controls it is something to look at. Test the diaphram with a hand vacuum pump. These diaphrams sometimes leak or rupture. Of course make sure the rod is adjusted correctly and that all the carb linkage is correctly assembled.

Aside from the carb, what about ignition timing? Are you getting 29 degrees at 2,900 rpm. Should be somewhere close to that with the vacuum advance disconnected. If not, check the centrifugal advance for being stuck.

 

If plastic cam for secondaries is broken (common) it will bog because it will get more fuel and little to no air. Secondary meter rods open very slightly causing rich condition. Also cam spring adjustment needs to be spot on. Adjustment spec. is carb. # specific. Also effected by converter or gear ratio changes. Vacuum breaks both primary and secondary, choke and linkage adjustment need to be diagnosed and set properly.
Joe