secondary air valve
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
this is from a paper by Lar's
Secondary throttles adjusted to not open fully:
Results in: Poor WOT performance.
Comments: The secondary throttle shaft is actuated by a link off the primary shaft that hits a lever on the secondary
throttle shaft. It is common for this to be misadjusted so that the secondary throttle blades do not fully open. Some
factory cars & carbs were intentionally set up to limit secondary throttle opening (like 1st-generation 400-powered
Firebirds) in order to limit horsepower for one reason or another. Check for this whenever the carb is disassembled
and adjust it by bending the contact tang on the primary throttle shaft.
Secondary throttles adjusted to not open fully:
Results in: Poor WOT performance.
Comments: The secondary throttle shaft is actuated by a link off the primary shaft that hits a lever on the secondary
throttle shaft. It is common for this to be misadjusted so that the secondary throttle blades do not fully open. Some
factory cars & carbs were intentionally set up to limit secondary throttle opening (like 1st-generation 400-powered
Firebirds) in order to limit horsepower for one reason or another. Check for this whenever the carb is disassembled
and adjust it by bending the contact tang on the primary throttle shaft.
This is in regards to the throttle blades in the throttle body. The OP is talking about the air valves in the airhorn.
The possible causes for this not opening are:
1. Choke pull off linkage (engine on at idle, or linkage is bound/hooked up incorrectly)
2. Some QJets have an air-valve lockout when the choke is cold
3. Binding between the blades and doors, as mentioned above.
4. Shaft rust could make it difficult to turn.
