I have a new Edelbrock 1901 and the secondary air flaps are being held shut by the choke pull off. Am I connecting something wrong?

 

That's how it's supposed to work - that's correct.

 

Yeah, it's a smog control so that the secondaries don't open until the engine is warmed up enough.

 

The car falls totally flat on its face when I go past 1/2 throttle which tells me the secondaries are opening but the air flaps are not.

How are the air flaps supposed to open when they are being physically being held shut by the choke pull off.

 

Oh but you deserve nothing less than " Advanced Engine Advise "

 

The secondaries actually pull the choke pull back. It works like a dash pot or dampener. It is part of the secondary control componenets.Go to www.corvettefaq.com and find Lars Q-jet tuning paper .It will walk you through the whole process.

 

Mick -
First, the airvalve is not a smog control item to keep the secondaries from opening until the engine is warmed up. And the secondaries don't pull the choke back.

The secondary airvalve is used because the Q-Jet does not have a secondary accelerator pump. The airvalve controls the opening rate and opening point of the secondaries in order to avoid a massive bog when you go into the secondary side. It does this by providing a controlled transition rate, as well as providing an initial fuel shot by momentarily staying closed while the discharge oriface is exposed to manifold vacuum through the open throttle blades below.

The airvalve is controlled by two features:
First, as you note, the choke pulloff holds it closed under normal engine operation. When manifold vacuum approaches atmospheric pressure (no manifold vacuum) as it does at wide open throttle (WOT), the vacuum signal to the pulloff is lost, and the pulloff extends. The rate at which it extends is controlled by a calibrated bleed hole in the pulloff. This allows the airvalve to open as differential air pressure across the airvalve forces it open at a rate allowed by the pulloff. The pulloff allows the airvalve to open; the airvalve does not pull the pulloff open.

Whereas the pulloff controls the opening rate, the secondary airvalve windup spring controls the opening point. There is an adjustable spring on the passenger side of the airvalve up underneath the airhorn. If this spring is not set tight enough, the airvalve will open too soon, and the car will bog. If the spring is too tight, the opening point is delayed, and a performance loss will be seen. The spring should be set initially to 3/4 turn.

Failure of either the pulloff or the spring to be connected or set up right will result in a premature opening point of the airvalve with a resulting bog.

 

l understand how the mechanical secondaries open. What is confusing me is the Air valve (Flaps) on top.

They are attachd to an arm that attaches to a vacuum choke pull off.

When the choke pull off has vacuum (car is running) it is pulled in completely and holds the arm tight which in turn keeps the air flaps from even thinking about opening with finger pressure let alone a change in vacuum from the secondaries opening? In other words they are being mechanically restricted.

The problem as I see it is, there is a constant vacuum being applied to the choke pull off.

Thanks I've read Lars paper before but I will re-read it again to make sure.

Lars, just read your post. Seems as though I'm not getting a drop in vacuum at WOT and the airflaps are staying closed under all conditions.

TIA
Mick

 

I miss worded my last response.. I know how it works , just not how to explain it.

 

Mick -
It's not possible to not get a drop in vacuum at WOT. When you go to WOT, manifold vacuum will drop, and the pulloff will relax - it's not possible for it to not do this unless you're not actually getting full travel out of your throttle linkage. Test your throttle linkage and make sure your gas pedal is really pulling the secondary throttle shaft to the wide open position (test this with engine off, of course...). If you are getting full travel out of the throttle, and if your choke is opening fully to retract the secondary lockout lever, the airvalve will function correctly - it's impossible for it not to.

Note that you cannot test this and observe it by "flicking" the throttle in neutral: The car must be under load and at WOT for the system to work. You cannot observe this function under the hood, even by flicking the throttle momentarily to wide open: the no-load on the engine will not drop manifold vacuum enough to allow the airvalve to open. This is not the case when the car is on the road.