Q-jet pump arm adjustment - Team Camaro Tech
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post #1 of 3 (permalink) Old Oct 1st, 05, 09:57 PM Thread Starter
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Question Q-jet pump arm adjustment

On the green accelerator pump arm there are two holes for the linkage. Before I rebuilt this q-jet, it was in the hole closest to the fulcrum point. (truck carb)
I noticed today that I reassembled it with the linkage in the outside hole in the arm.

What is the purpose of this adjustment, and which hole is best to use? I'm assuming the two holes will move the pump different distances and that the furthest linkage point will give the most movement of the pump.
Can someone enlighten me please?

Also, I want to make sure the secondaries are operating properly....
Operating the throttle by hand to WOT, the secondaries won't open until the choke is set almost 100% open. This is done by the heat riser spring setup on the intake. I foget the name of that device. Until the engine is at operating temp and the choke is wide open, the linkages prevent the secondaries from opening at all.
The upper secondary butterflies don't open at all when operating the throttle by hand, no matter where the choke is. That is a function of vacuum, correct?

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post #2 of 3 (permalink) Old Oct 1st, 05, 10:59 PM
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Wink Re: Q-jet pump arm adjustment

Quote:
Originally Posted by HwyStarJoe
On the green accelerator pump arm there are two holes for the linkage.
What is the purpose of this adjustment, and which hole is best to use?
I'm assuming the two holes will move the pump different distances and that the furthest linkage point will give the most movement of the pump.
Can someone enlighten me please?

Also, I want to make sure the secondaries are operating properly....
The upper secondary butterflies don't open at all when operating the throttle by hand, no matter where the choke is.
That is a function of vacuum, correct?
Wow - you missed 2 out-of 2 on that test Joe

The inner hole on the arm will increase the fulcrum effect on the arm and result in more travel at the end of the lever and a longer (read "richer") accelerator pump piston depression.
So - Inner hole = richer shot, Outer hole = leaner shot.
Usually the outer hole is specified for cars and light trucks except for higher altitudes and colder weather driving - but, the spec. sheet with the rebuild kit should give the recommended hole position.

The Secondary Air Valve operation can be a bear to check on the vehicle when your trying to watch it operate under the hood.
It takes a fairly large amount of air flow through the carb & the secondary throttle valves open to get the air valve to open.
The secondaries are limited to operation for the last 35~40 deg. of throttle opening by the linkage system. They also will not opeate if the choke is "on".
I usually don't worry about the air valve unless I'm working with a 'bogging' situation or the secondaries are coming in late for some reason.
There is a spring wind-up adjustment* for the air valve that sets it's resistance to opening. This spring holds the valve closed until the air flow is great enough to overcome the valve setting and also pull fuel from the secondary circuit. As the air valve opens, it also activates the secondary metering rod system which increases the fuel flow to the discharge nozzles.
* - You can adjust the spring if for some reason the valve is coming in to soon or not soon enough... Adjusting the spring is easy - getting it right, not so much, at times...
If you are having a certain problem with the secondaries or the carb. maybe we can talk you through it.

BTW - if you want an easy indication of the secondary air valve actuation, just remove the air cleaner and take the car out to an open road area and stand-on-it...
That hollow moan you hear as the air valve opens and your engine starts to suck for all it's worth is a good indication it's opening...

Hope some of this helps;
John

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post #3 of 3 (permalink) Old Oct 2nd, 05, 05:03 AM Thread Starter
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Re: Q-jet pump arm adjustment

John to the rescue AGAIN!

Well, since it's on a 350 that's going in a Camaro, I guess I'll switch it to the richer position and see what happens. We're only at 500' above sea level here.
You're right about the adjustment listed on the sheet.... I missed it. It says to use the inner hole for EVERYTHING from 350 to 454 (on a truck) and any car with a 350 to 454.

I knew about the adjustment for the air valve. I have adjustment procedures I'm going to go thru when the time comes.

Thanks John!

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