You should know that they will not open in the driveway, and there is no way the car would get to redline on the road without them opening.
Secondaries not opening with a slow foot
Thread Starter
Racer
Joined: Feb 2009
Posts: 265
Likes: 0
Secondaries not opening with a slow foot
Hi all,
My '71 427 sb has a Performer RPM 850 Q-jet. Runs great, goes like stink if I floor it- no bog etc. on the secondaries opening, but I've noticed the secondaries never open if I open them slowly. It'll go all the way to redline like that.
My '71 427 sb has a Performer RPM 850 Q-jet. Runs great, goes like stink if I floor it- no bog etc. on the secondaries opening, but I've noticed the secondaries never open if I open them slowly. It'll go all the way to redline like that.
Thread Starter
Racer
Joined: Feb 2009
Posts: 265
Likes: 0
With at least 500 hp, when I floor it, I KNOW they open because you get pushed way back in the seat, it screams to redline, the front end lifts, the steering gets real light, and it scares any passengers onboard.
When I get it to the floor slowly and even after it's been held to the floor, none of the above happens, and it acts and feels like it's only running on the primaries. I can still push it to redline.
When I get it to the floor slowly and even after it's been held to the floor, none of the above happens, and it acts and feels like it's only running on the primaries. I can still push it to redline.
Thread Starter
Racer
Joined: Feb 2009
Posts: 265
Likes: 0
It's pretty impressive just on the primaries- 427 small block stroker has lots of torque.
I should mention one time I was already higher in the rpm's, floored it, nothing happened for a second- it wasn't a bog or hesitation, then the secondaries kicked in like a mule- never get any bog. Adjusted the air valve on this new engine not too long ago- turned it back clockwise about 1/8th turn from where it would hesitate slightly and it's been great that way ever since until I realized how it acts if I open it all the way slowly. Air valve was hanging up in the past on the edge of the carb, worked on that while ago and still doesn't seem to stick whether engine's hot or cold.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
They are a demand type carb, if the intake flow requires cfm they will open enough to give it whether it is fast or slow and a 427 reqiures cfm.
The only way to really tell is to prop the hood open with the air cleaner off and watch. I bet at redline, they are open , or hung up on something if not.
If you are really used to the car you can hear them when open.
The only way to really tell is to prop the hood open with the air cleaner off and watch. I bet at redline, they are open , or hung up on something if not.
If you are really used to the car you can hear them when open.
Thread Starter
Racer
Joined: Feb 2009
Posts: 265
Likes: 0
They are a demand type carb, if the intake flow requires cfm they will open enough to give it whether it is fast or slow and a 427 reqiures cfm.
The only way to really tell is to prop the hood open with the air cleaner off and watch. I bet at redline, they are open , or hung up on something if not.
If you are really used to the car you can hear them when open.
The only way to really tell is to prop the hood open with the air cleaner off and watch. I bet at redline, they are open , or hung up on something if not.
If you are really used to the car you can hear them when open.
Oh, you mean drive it wide open with the cleaner off? Got an L88 hood- that'll make it a lot easier to watch them at least.
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Thread Starter
Racer
Joined: Feb 2009
Posts: 265
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Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Put a Holley or Demon DP with mechanical secondaries on it and you know they open when you put your foot into it. Just a suggestion 
Melting Slicks
Joined: Jul 2006
Posts: 2,292
Likes: 494
From: Salmon Arm, BC
If the rear two screws on the top plate are too tight binding can occur with the secondary air flap. I've seen this occur on two different carbs.
Check and make sure there is no binding,and if there is clearance it.
Check and make sure there is no binding,and if there is clearance it.
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
Quadrajet secondaries are mechanical, so technically, unless the lock-out is holding them closed, they open when you push the pedal far enough.
The air valve may be sticking, or as you accelerate slowly, you just don't feel it open because it is opening slowly according to engine demand. As mentioned earlier, you could check if you can actually see the air valve as you drive (hood and filter out of the way).
God bless, Sensei
The air valve may be sticking, or as you accelerate slowly, you just don't feel it open because it is opening slowly according to engine demand. As mentioned earlier, you could check if you can actually see the air valve as you drive (hood and filter out of the way).
God bless, Sensei