Secondary Air Valve Adjustment

I am confused regarding adjusting the Secondary Air Valve spring. I think my secondaries are opening a little late and my mechanic said to tighten the spring. I guess I don't understand the operation of this system as it seems you would want less spring tension to open earlier. o No:

 

999 times out of a 1000 the secondaries open too SOON, in which case the mechanic is correct. To make them open sooner, you would loosen the tension on the spring.

Symptomatic of opening too soon - bog or hesitation when secondary opens
Symptomatic of opening too late - continuous power, but weaker than it should be.

While each carburetor has its own setting (and should be checked in the service manual) MOST of the Q-Jets have a setting of 1/2 turn past the point where the airvalve just seats. This setting assumes that the airvalve tension spring is not fatiqued. The airvalve tension spring and the airvalve cam should ALWAYS be changed when the carburetor is rebuilt.

Jon.

 

That's right...

Also, check to make sure that the secondary air valve moves freely and is not binding / rubbing up against the inside face of the carb body.

 

secondaries

Also make sure the choke lockout rod is set correctly or they will not open at all.

Mikey

 

As long as you don't floor it until the engine is warm, you can leave the choke secondary lockout link off.

Make sure the vacuum dashpot at the front of the carb is pulling in when the engine starts, if it isn't it'll let the secondaries open too quickly, sometimes bouncing open/closed.

On the underside of the carb airhorn (top), at the rear passenger side, there is a tiny set-screw that locks down the air valve spring. The spring pushes/pulls a pin in the end of the air valve shaft, trying to close the air valve. Loosen the setscrew, then with a tiny flathead screwdriver you can adjust the spring. 1/2 turn past the point that the spring *just* engages the shaft pin is a good starting point.

The secondary opening rate is controlled by the vacuum dashpot and the spring, both working "against" the airflow trying to get through the secondary side of the carb. Great self-regulating system when working. :TU:

 

There Is Also A Vacumn Diaphram That Controls Secondary Air Valve Opening. Best Advise Is To Pick Up A Copy Of A New Q-jet Book Out By Cliff Ruggles. It Explains How To Tune And Modify The Q-jet, Lots Of Pictures That Should Make Things Crystal Clear. Good Luck