Stupid Q-JET QUESTION
Thread Starter
Instructor
Joined: Dec 2007
Posts: 245
Likes: 2
From: Jersey shore NJ
Stupid Q-JET QUESTION
I do not know much about the Q-jet and was just wondering if the secondary upper butterfly is supposed to open when the front choke opens? Or does it open with vacum when the secondaries open?
Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
First part... Actually no. But there is a connection. The upper secondary butterfly,(air valve), as well as the secondaries, are locked out until the choke heats to operating temperature.
At that point it does open when the secondaries become machanically opened, sucking all that air in making that unique Q-jet sound, and exceleration
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Heh fellow jersey guy. Short simple version......
First part... Actually no. But there is a connection. The upper secondary butterfly,(air valve), as well as the secondaries, are locked out until the choke heats to operating temperature.
At that point it does open when the secondaries become machanically opened, sucking all that air in making that unique Q-jet sound, and exceleration
First part... Actually no. But there is a connection. The upper secondary butterfly,(air valve), as well as the secondaries, are locked out until the choke heats to operating temperature.
At that point it does open when the secondaries become machanically opened, sucking all that air in making that unique Q-jet sound, and exceleration
However, as a clarification to the above, the secondary air valve only opens when the secondary butterflies are open AND the engine is flowing enough air to pull the air valve open. This WON'T happen with the engine off, or with the engine running in neutral, but only with a load at higher rpm such at WOT and rpm above 3,000 or 4,000 rpm.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
The upper air valve opens relative to the amount of airflow through the secondaries. It is vacuum "switched" (a vacuum system allows that valve to open), but the amout of movement of the valve is determined only by the amount of airflow being pulled through the secondaries. Thus, it is airflow regulated, not vacuum regulated.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
P.S. This 'regulated airflow' approach to the operation of the Q-jet secondaries is one of the positive design differences in the Q-jet. The carb airflow is regulated by demand, rather than by designed capacity. The Q-jet only flows what your particular engine needs...up to the max. capacity of the carb. And most Q-jets are rated 750 cfm. But, you can put a 750 cfm Q-jet on a 650 cfm engine and it will work just fine (with proper jets and rods, of course).
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