How far should quadrajet secondary throttle plates open at WOT? Should they be completely vertical? Mine aren't.
I have been trying to demystify the Q-Jet on my O/T motorcycle. I bought Cliff Ruggles book which, I hope, will be helpful. The secondary air doors do not, necessarily, open all the way. They only open as far as needed, based on vacuum at the secondary throttle plates. One important thing that I learned is do not monkey with them and, especially, do not remove the vacuum break, thinking it is hindering the air doors. It is vital
When i was tuning a quadrajet i find some very helpful clips at youtube. As i remember the secondarys should not open full out.
How far they open depends on the original application for the carb. Cliff's book explains this. The amount they open is one of the many tunable features of those carbs.
The secondary throttle plate(which is on the base of the carb, should mechanically open fully as the primary throttle plate does. Do not confuse these with the secondary air valve on top that is controlled by spring tension and vacuum.
This is correct many only opened only 3/4-7/8 of the way. For sake of ease, Only the high performance models opened fully from the factory. They also rated CFM on the amount they opened originally. This can be modified to open fully
Most dont open all the way.. if you want you can adj linkage to allow it 90 degrees. If I remember right they left them not open all the way to try to even out the flow to the front cyls because of the small primaries.
they limited most of them for emmision purposes . some models they put restrictions on the upper doors to limit the cfm flow to make them leaner for cat converters , the the lowers for performance should be 90* as Doug Roe states ( Dougs book is the bible as he was a rochester engineer RIP )
If I remember right, it takes very little modifications to a Q jet to make it a much better carb. Make sure the secondary opens all the way, and make it easier for the top ****erfly to open. adjust the metering rods to open sooner also helps.
Secondary ****erflies were used to tune the carb to smaller engines by reducing the opening. But if you are looking for performance, by all means open them up. But if you do, you will most likely need to tune the air valve spring opening and maybe the jets and rods, also.
Fwiw, the 400 'Bird's Q-Jets were limited from the factory so that their engines wouldn't produce as much power as the Goats!! My big-headed B-I-L had a '67 'Bird with a 400/4-speed in it that he trashed. He would screw the Q-Jet up, I would reset the top rear "door" and he would repeat. He couldn't stand that I knew how to set them!! The only reason I know this is because his Son told me on the QT one Sat. morning.. pdq67
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