Q-jet on my C3 a 69 350/350

[james Kekeisen]

My secondary's air valve never opens on my carb regardless of how far the throttle is open. The vacuum break assembly prevents it from opening (hot or cold). If I force it open with my hand the Vacuum break assembly shaft will move outward but then when I release it, it goes right back in. Is this normal? What is the steady state position of the vacuum break shaft all the way into the assembly or all the way out?

Thanks, Jim

[Bill Clupper]

Re: Q-jet on my C3 a 69 350/350

Once the engine is running, the vacuum break opens the choke slightly. There is also on many Q-jets another device that is there to slow the opening of the secondaries to prevent engine "bog" under accelleration. I assume this the system you are actually looking at. apply a vacuum to the nipple coming from the can and see if it retracts with a vacuum. If so, it is OK. The opening of the secondarys on a Q-jet also interacts with the choke being fully opened, and the adjustment on the spring that holds the secondary air valve closed.

[Bill Clupper]

Re: Q-jet on my C3 a 69 350/350

Once the engine is running, the vacuum break opens the choke slightly. There is also on many Q-jets another device that is there to slow the opening of the secondaries to prevent engine "bog" under accelleration. I assume this the system you are actually looking at. apply a vacuum to the nipple coming from the can and see if it retracts with a vacuum. If so, it is OK. The opening of the secondarys on a Q-jet also interacts with the choke being fully opened, and the adjustment on the spring that holds the secondary air valve closed.

[Clem Z.]

Re: Q-jet on my C3 a 69 350/350

the vacuum break that controls the secondary air flap will release when you floor the gas pedal under load on the road because the vacuum in the engine drops and the vacuum break will release the secondary air flap to open controlled by the size of the orifice drilling in the vacuum break. the air flap will not open just reving the engine setting in your garage.

[Clem Z.]

Re: Q-jet on my C3 a 69 350/350

the vacuum break that controls the secondary air flap will release when you floor the gas pedal under load on the road because the vacuum in the engine drops and the vacuum break will release the secondary air flap to open controlled by the size of the orifice drilling in the vacuum break. the air flap will not open just reving the engine setting in your garage.

[james Kekeisen]

Re: Q-jet on my C3 a 69 350/350

Clem, you answered the question I was really after but didn't ask! Revving it by hand it doesn't budge, thanks. My lack of get up and go must be something else. It runs smooth, is timed per the full advance advice on the board, and has all new or refurbished parts. Is it posssible that the Holley high rise single plane intake and edelbrock carb that I replaced with a stock Q-jet and original intake makes that much difference?

Jim

[james Kekeisen]

Re: Q-jet on my C3 a 69 350/350

Clem, you answered the question I was really after but didn't ask! Revving it by hand it doesn't budge, thanks. My lack of get up and go must be something else. It runs smooth, is timed per the full advance advice on the board, and has all new or refurbished parts. Is it posssible that the Holley high rise single plane intake and edelbrock carb that I replaced with a stock Q-jet and original intake makes that much difference?

Jim

[Clem Z.]

Re: Q-jet on my C3 a 69 350/350

the Q jet is a 750 CFM carb and it should give you better throttle response at lower RPM than your other setup. on the passengers side of the carb there is a stop on the air valve shaft that makes contact with the carb main body at wide open throttle,move the air flap by hand with the engine off to see where this stop contacts the carb main body,put a small dab of grease there. take the car for a full throttle run after it has warmed up, then check the dab of grease to see if the air valve stop has made contact. if not you are not opening the secondary air valve.

[Clem Z.]

Re: Q-jet on my C3 a 69 350/350

the Q jet is a 750 CFM carb and it should give you better throttle response at lower RPM than your other setup. on the passengers side of the carb there is a stop on the air valve shaft that makes contact with the carb main body at wide open throttle,move the air flap by hand with the engine off to see where this stop contacts the carb main body,put a small dab of grease there. take the car for a full throttle run after it has warmed up, then check the dab of grease to see if the air valve stop has made contact. if not you are not opening the secondary air valve.