when I hammer the gas the car hesitates and the secondarys do not open, even when sitting in the driveway, any ideas? Q-jet 77.

 

I don't think the secondaries will open if reving the engine while its parked.

 

on my 75, if you crack the throttle real fast while in park they start to open, not reving the crap out of it.

 

I'm not a q-jet guy, but I do have one on my truck.

I assume there are two versions: a vacuum secondary or mechanical seconday. My truck's is mechanical and if I WOT rev it in neutral, the top plates on the secondary side crack open about 1/4". The throttle plates in the base casting are all the way open, but the engine can't pull enough vacuum w/o load to open the spring-loaded plates on top.

On a car with vacuum secondaries, you probably wouldn't even get that.

You should hear it when the secondaries open. Regardless, I was always told to wire them shut in order to verify function.

Your bog could be due to a lean condition from the secondaries snapping open TOO fast...but it could be any one or several of 20 different things.

 

mine are vacs and I did read Lars' papers on these things, tons of info, you can get that deep sound like they want to open, I will read again.

 

Assuming you have a q-jet, I would look at the secondary flap adjustment. Lars is the expert but untill he shows up I would be looking at the secondary air flap adjustment. The flap is spring loaded and the vacuum pull off holds it closed untill the engine demand requires it to open.

When you stomp on the gas while driving, the flap will crack open a tiny bit exposing 2 tiny holes near the edge of the flap. The air rushing by the holes acts like a secondary accelerator pump drawing in added fuel. As the manifold vacuum drops under the added load, the vacuum pull off will relax allowing the secondary air flap to open further kicking in the secondaries. That is when it finaly takes off.

If the air flap spring tension is too loose, the flap will open too soon, causing a bog. The vacuum pull off needs to be adjusted too so the fuel will be pulled in while the flap is just cracked open. You need the specs for your carb to set these. A typical air flap spring tension setting is about 7/8 of a turn past closed. This is a common spec if you do not have the manual and need a place to start.

Once again, I aint no expert but this might help some.

Paging LARS! We need the master!

-Mark.

 

All Q-Jets are mechanical secondary carbs. The only vacuum secondary carbs on the market are Holley and BG. There are no vacuum secondary Q-Jets.

The Q-Jet secondary is controlled by use of an airvalve, but it is not vacuum actuated. It is allowed to open through loss of vacuum signal to the choke pulloff, but this does not make it a vacuum secondary.

Since the Q-Jet is purely mechanical, there are only 2 things that can prevent secondary opening:

1. Secondary lockout lever not retracting. On the passenger side of the secondary throttle shaft, there is a lockout lever that prevents the secondaries from opening if the choke is not wide open. Verify that the lever is retracted when the choke is open (and verify that your choke is opening fully when hot).

2. Inadequate throttle cable travel. Have someone push the pedal to the floor (engine off, of course) and observe the throttle lever. Once the pedal is to the floor, see if there is more travel left on the lever and see if the secondary throttle shaft is fully rotated to the wide open position. If not, fix your cable and bracket.

You cannot see the secondaries open on a Q-Jet by rev'ing the engine in neutral - there is not enough airflow requirement to push the airvalve open under a no-load condition. If you rev the crap out of it, you can sometimes see the airvalve just barely crack open, but there is no point in doing this: the secondaries will open if the 2 points noted above are taken care of.

 

Thanks Lars, and all, will check it out.