Car is 72 Stage 1 with about 600 hp, rebuilt stock Rochester 850cm, 7042242. At launch with WOT, the engne will bog until I let off for a second, and then it will launch. Does it every time. I have heard that the squitters need to be enlarged. Has anyone changed the squitters on this carb? Are larger squitters available? I also understand that the secondary air doors may be letting in too much air too soon. Any help is greatly appreciated. Thanks, Terry Fort Pierce, FL
Theres a spring you can adjust that controls the opening on the secondary flap. I had to play with mine a bit until I got rid of the stutter.
I'm thinking secondary flap as well. Start tight and work out little by little. It will be worth the hassle.
Terry ask Cliff at http://www.cliffshighperformance.com/ Go on his forum he will answer all questions he is the Q-JET man:3gears:
You can enlarge the squirt by opening them up with tiny drill bits. This is rarely needed however. Probably the air flaps as mentioned. I modify them myself on these carbs for smoother opening. The tension spring and primary pull off are what also need changing. You can adjust the spring tension. Also get an adjustable primary pull off. A correctly modified quadrajet can handle your power, but needs many tweaks to be the best. They can be modified to flow more cfm also. I have an adjustment sheet I can email you if you are interested. It may help you adjust out the bog you have.
If you are really in the 600 hp range, a stock rebuilt quadrajet will not due. These carbs were emmissions restricted from the factory. There is a good chance you can melt the pistons. Stop immediately and get professional advice from cliff or one of the other quadrajet experts on this sight. For the record the accelerator pump discharge restriction would have to be drilled oversize since it is predrilled at the factory. Good luck
In addition to air valve tension, you can look at the POE circuit and potentially make some changes there...As you look at the airhorn at the front of closed secondaries, if there is a tine hole above 1/16" inch above the valve, you can notch the leading edge of the valve by about 1/8", kinda like Pontiac did, just not as big. Those holes in the airhorn are the squirters you mentioned, and if they initially hit the top of a closed valve that does you no good in transition, the notch give it a place to slip through... These guys are correct about taking to Cliff before you melt a piston, but set up correctly these carbs can easily support 600 HP - don't give up on it.
You guys are just great. This is a huge help. I'm all over it and will tackle it this weekend. Thanks much, Terry
I agree 100% with this one. Recalibrate for your setup and youll be surprised the difference you feel.
you can remove or disable the secondary dash pot , makes it easier to dial in the opening of the secondaries imo , just tighten the spring more I however do agree that with a solid 550hp+ id go to holley ,, no primary rods with holley jets is another way to.move more fuel thru it, also the secondary air doors can affect top end A/F by reducing door angle to richen the mixture
I didn't catch it was a real Stage 1 carb....if that's the case, start with a different core to modify...I know Ken at Everyday has them on the shelf for reasonable money (and they're PRETTY, featuring his new coating process in the colors of your choice....) and can modify to your spec...
https://www.youtube.com/watch?v=XMtZNOtxEec Both of these Firebirds use Q-jets, the FAST Class FB in the right lane uses an engine making WAY past 600hp. The big Buick 7042242 is PLENTY of carb for what you are doing, it just needs some help in a few areas to get it dialed in......Cliff
UPDATE: I tightened the secondary air door spring, and what a difference! No more bog. Launches at WOT with no hesitation. I loosened the allen screw underneath the spring and turned the spring adjustment screw 1/4 turn clockwise, which put more tension on the spring. I also freed up the air doors which may have been sticking open. Thanks to everyone who contributed with your expert knowledge. Glad to have this resolved. Terry
Go news! A choke pull-off that releases too quickly will make secondary tuning at the track difficult. A lot of spring tension will be required prevent stumble/hesitation/bog on full throttle starts with good traction if the pull-off is to quick. A weak spring and/or worn cam will also make secondary tuning difficult. Don't forget to put some grease on the pin where the spring slides to help out as well......Cliff
Love reading these posts. Learning a lot about Qjets. Also using Cliffs book as I stumble through a rebuild. Sent from my iPhone using Tapatalk
