First put a pocket screwdriver in the adjustment screw circled in blue, note the position of the slot, so you know how much and which way you wanna go, I make adjustments in 1/8 turns, clockwise is tighter, counterclockwise is looser. After you have your screwdriver in the adjusting screw, insert your allen key in the set screw circled in red, move the allen key towards the firewall to slightly loosen the set screw, then move your adjusting screw whichever way you decide, then move allen key towards the front of the car (tightening set screw) Go out and drive it see how she feels.
What behavior of the secondary is this actually adjusting? Is this an opening and/or closing stop adjustment or something else?
Its adjusting the spring tension on the flaps/doors. If you look to the left of the circled in red set screw, you can see the tang of the adjusting spring sticking out. The spring tension adjusts how fast the flaps open. The actual secondary throttle plates are below those flaps and are connected to the primary throttle plates, they start to open when the primaries are 60 to 70% open, IIRC. The Quadrajet is a mechanical secondary carb, NOT a vacuum secondary. If you tighten the set screw, the secondary's take longer to open, as engine vacuum drawing on the flaps has greater tension to overcome. If the tension is too little, the flaps drop open soon after the secondary throttle blades go wide open creating a HUGE vacuum leak with not enough fuel to fill the hole....BOGGGGGGGGG. There is no dedicated secondary squirter (accelerator pump) The fuel is drawn by vacuum after the secondary rods are lifted (in simple terms)
Thank you John. I still have reservations on the Q-Jet behaving on the track WITH DR's (traction) as the traction loads the engine verses just wheel spin with street tires. A first gear downshift @ 20 mph and under results in wheel spin, so the engine doesnt really see any load.
Agreed! Thanks Mark! I'm going to make some adjustments to my air doors and see how it goes from there. Hopefully I don't have to build an Arc to save it from drowning. We had 5"+ of rain the last 24 hours and it's supposed to rain every day till Friday! That's not supposed to be a river...Its I94 lol If I can get this qjet dialed in, I should be able to give those Holley boys a run for their money
WOW Kevin, how the hell yah supposed to get a boat under that bridge? The engineers really dropped the ball on that one
Need to pump that to Washington. Guess you guys are stuck at home a few days. Can't you put bigger shooter in the QJet, You going to tell me delaying the flap door does not keep the car from bogging? It should come out of the hole like a freight train on those two front barrels then the back two should start to open rapidly. Maybe you should try a 4 hole spacer Wonder if they have a taper spacer for those carbs. I bet you stick a Thermoquad on there and it wont bog I bet that bitch will rock Did't you guys read about the 455's back in the 80's LOLOL guess you all weren't here then LOL. When I ran it on the 350 it boiled the tires out of the hole and ran my best time spinning the tires. That was with my old Comp Cam 268 and a bone stock 71 no comp engine headers only with duals no convertor and a 373 gear 14.89 boiling the tires. Next time down track it was flooding engine and that was the end of it cracked the crank and here we are today. The floats were too high. I never did anything with that Thermoquad again sitting in a box all apart. There was one for sale in the GS club mag a month ago or so and was used on the old 350's of the Ken Bell days. That would have been perfect for that SP3 but I bet the thing is gone now. I always liked it when you flapped those throttles it sprayed some gas in there...all over the place!
Fwiw. Air flap opening rate is also controled by choke pull off. Apply vacuum to pull off and release. Alot of 'factory' one are slowish at about 3 seconds. Some setups like quicker at 1 1/2 seconds. Requires opening restriction in pull off or getting one from Cliff or others. Were talking like .016 holes. Or you can open up larger and make small inserts for vacuum line with various sizes holes so you can 'tune' opening rate.
Cliff sells a modified pull off for smoother air door opening, https://cliffshighperformance.com/product/choke-pull-off-67-70 I don't see it on his site, but he also sells, or did sell, a pull off with an inline vacuum valve to adjust the pull off resistance via a vacuum adjustment.
As far as I know you cannot buy the proper slow pulloff that a Buick likes. I see Cliff modifies them, I do also for the carbs I do for folks. I don’t believe you can get a fast operating pulloff to function properly with just a spring adjustment on the flaps. All of the ones I do open smooth, no hesitation. Mark, is that an open plenum intake you are running?
^ok, it may need more pump with the open plenum but I’d approach it slow and see how good you can get it because once you open the pump shot it’s tough to go back.
If the combination of the spring tension on the air door, the time the vacuum pull off releases are set up correctly, you won’t bog. It should be a smooth seamless transition when you nail it. You will bog if the spring tension is too loose or the choke pull off releases too quickly. Use a vacuum pump to check the choke pull off as an old unit may not be holding vacuum. The choke pull off is a key part of the secondaries to operate smoothly - no bog.
X2 on the choke pull off. You might need to get creative and block the airway some to ensure it does not release too quickly.. I think 2-2.5 seconds is the sweet spot? That in relation with secondary air valve spring adjustment will net you a smooth transition
