I have a 4bbl HO carb on a 305 engine. I have a hunch that only the 2 primary barrels have been opening during my whole ownership of the car. Not just me but many people think this to. I can never recall the 2 secondary barrels ever opening up. i just got done opening up the carb last night and diddnt find anything. Do you have suguestions to either fix or test to see if this is true?

 

With car in the driveway/garage/parking space and engine turned off, do the following:

1) Open hood.

2) Remove air cleaner and set it off to the side.

3) Plug the vacuum nipple that the air cleaner vacuum hose connects to.

4) Close hood.

5) Find an open stretch of road, preferably paved and nearby. Starting from about 10 mph in 1st gear, floor it. Run to redline, shift to 2nd, floor it again. Repeat until you reach the speedlimit.

6) Return home and reassemble in reverse order.

When you floored it, did you hear: a) a manly "waaaaaaah!" sound? Perhaps it fell on its face, and then made that sound? Or was it: b) a sissy "heeeeeeeh" sound?

If a), your secondaries are opening. If b), they are not.

Do not attempt this in your driveway or garage. It will not yield useable information.

 

Oh, forgot to mention: The engine has to be fully warmed up before you begin Step #5.

 

Ok i did as you said. I was having trouble distungusihing between sounds but i am pretty shure that it was more of a heeeeeh sound. It just sounded like an engine under a lot of stress. There was nothing special. I mean if the secondaries kicked in is it a very obvious sound? Do they just open at once or do they gradually open? If i was to go with a choice it would be b.

 

They are supposed to gradually open. If you feel them open up, they're opening too quickly. If you aren't hearing the deep "roar" with the air cleaner removed, then perhaps they aren't opening properly.

There are two reasons your secondaries may not be opening: 1) The throttle body secondary valves may be held shut; or 2) the secondary air valve may be held shut.

I'm betting #1.

There is a little device on the passenger side of the carb, on the throttle plate, that locks out the mechanical secondary valves when the engine hasn't warmed up. This is accomplished without any action, i.e., this is the default mode. In order for the secondaries to be allowed to open, the choke must be fully opened, which allows a green weight/lever to fall, which pushes this little locking device away from a pin on the secondary throttle shaft. So, first, make sure the choke is opening all the way, and second that the little green weight/lever is moving freely and dropping all the way down. 3rd, if the above are true, that the lockout mechanism is clearing the secondary shaft pin.

The air valve not opening is less likely, but still possible. It is held closed in two ways: 1) By the choke pull-off (believe it or not), that holds the AV closed until vacuum drops; and 2) an adjustable tension spring built into the AV shaft. There is a tech article accessed via links from the TGO home page that talks about adjusting that item (article title something to the effect of getting the most out of your computer controlled q-jet). The choke pull-off would have to be stuck in the applied position, something I have never seen.

 

The link is also in the Sticky https://www.thirdgen.org/techbb2/sho...hreadid=101977 above.

 

Thanks for your help. I did read the article and i adjusted it last night. I turned the spring so there was zero tension but there was still no results. I also replaced my choke pull off because it had a severe vacume leak. Just a little insight on what i have done. I will check what you sugested and get back.

 

I know i have heard of the secondaries being delayed. Is there a possible way to advance the opening of them. They could be opening just not soon enough. Some guys had this problem they just diddnt say how to fix it.

 

If you have zero tension on the AV, the only possibilities are the pull-off and lockout tab.

Unless something is seriously binding. A possibility if the air horn, main body, or throttle body have been distorted in one fashion or another.

 

On my old Q-jet the choke had a mechanical linkage that blocked the secondary throttle plates from opening. Not the air valves, but the actual butterflys. It was on the driverside between the shaft and the choke. Bent the little pin on mine that kept hanging up and I had secondaries.

 

I have a quadrajet that the bakelite cam that opens the secondary air valve was broken on. Basically made it a two barrel. However, once I fixed the problem my gas consumption went up oddly enough

 

Well i have been thinking about buying a new carb for a long time. Right now its a computer controlled 4bbl HO carb on my 1983 z-28 305. Any suggestions, i dont know what will work.

 

from five7kid
"5) Find an open stretch of road, preferably paved and nearby. Starting from about 10 mph in 1st gear, floor it. Run to redline, shift to 2nd, floor it again. Repeat until you reach the speedlimit."

can an l69 redline without its secondaries? the primaries can't deliver that much cfm can they?

 

I fixed the problem. They were getting stuck closed and with a few adjustments you can definatly hear them open now. My car is responding better than it ever has. Once again thanks for helping me with yet another problem.

 

There is a link between the primaries and secondaries on the driver's side, but that's what actually opens the secondaries.

The "little pin" is on the passenger side.

Morbid, what exactly did you adjust?

 

Well first of all i replaced about 4 vacume hoses and then opened up the carb. Whoever rebuilt the carb for a few hundred was retarded. The thing was a mess inside so i just cleaned it out as best i could. They must have only changed the gaskets and called it a rebild; what a rip off. I also adjusted the AV flaps and ironically enough freed up the badly coroded secondary linkeage. Put it all back together and i had secondaries. Too bad they are hard to hear with the air cleaner back on.