Q jet users
Thread Starter
Racer
Joined: Jul 2006
Posts: 337
Likes: 10
Q jet users
I just wanted to share this concerning the Q jet. Mine was running great overall, but I felt it could be better, mainly in the secondary area. I had no problems.....no lean sag, seemed to come in OK....
So....I screwed with something that was working fine, and gained a very noticable boost in performance. I spent 45 minutes and filed away an area at the top edge that the air door seemed to be hanging on every so slightly. This was just a tiny 1/4 long area....that took maybe ten minutes. The rest of the time was spent checking the vacuum dash pot orifice size and drilling it out to .015 to allow the air door to open sooner when called for. What a difference when you step on the gas! They are opening just perfectly to pour in that extra power with having to floor the petal.
As they say, it's all in the details !!
So....I screwed with something that was working fine, and gained a very noticable boost in performance. I spent 45 minutes and filed away an area at the top edge that the air door seemed to be hanging on every so slightly. This was just a tiny 1/4 long area....that took maybe ten minutes. The rest of the time was spent checking the vacuum dash pot orifice size and drilling it out to .015 to allow the air door to open sooner when called for. What a difference when you step on the gas! They are opening just perfectly to pour in that extra power with having to floor the petal.
As they say, it's all in the details !!
Pro
Joined: Jan 2005
Posts: 539
Likes: 3
From: Twin Cities Minnesota
pictures??? My 76 seems to run good also but seems like it should be better. I have been trying to decide if my 30 year old quadrajet should be put out to pasture.
Glad to hear yours is running stronger..
Glad to hear yours is running stronger..
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
By "air door" do you mean the secondary air valves? Glad you ID'd something that could retard their opening.
You can adjust the SAV's to open sooner or later. You'll need a 3/32 allen wrench (I think that's the size) and a small flat-head screwdriver. You'll see where it's to be adjusted on the passenger's side of the SAV shaft. Simply unlock the set screw (with the allen wrench,..the screw faces down) and either tighten or loosen the flat-head adjusting screw. Try 1/8 of a turn either way (tighter will slow the opening of the AV's,..looser with make them come in quicker). You won't need to turn the screw more than a half turn. DON'T ALLOW THE ADJUSTING SCREW TO COME UNWOUND!,..it's srping loaded.
Then lock in the set screw (allen wrench again) and take her for a test drive. You'll know when it's just right.
Good luck!
You can adjust the SAV's to open sooner or later. You'll need a 3/32 allen wrench (I think that's the size) and a small flat-head screwdriver. You'll see where it's to be adjusted on the passenger's side of the SAV shaft. Simply unlock the set screw (with the allen wrench,..the screw faces down) and either tighten or loosen the flat-head adjusting screw. Try 1/8 of a turn either way (tighter will slow the opening of the AV's,..looser with make them come in quicker). You won't need to turn the screw more than a half turn. DON'T ALLOW THE ADJUSTING SCREW TO COME UNWOUND!,..it's srping loaded.
Then lock in the set screw (allen wrench again) and take her for a test drive. You'll know when it's just right.
Good luck!
Thread Starter
Racer
Joined: Jul 2006
Posts: 337
Likes: 10
Yes, I adjusted what you mentioned last summer to stop the lean hesitation....they were opening too soon. I could tell the engine "wanted" more CFM at throttle openings less that full throttle, which is basically the only time mine were opening, unless going up a hill.
All the adjusting I referred to involves the "air door" at the top. If you pushed it open manually with engine off, you could feel a slight hang up ....but then it was fine. Both valves's outermost edge was binding ever so slightly on the top cover casting...IE the throat at, and around the secondary air doors. This was possible causing a slight delay. The big improvement was gained by opening up the bleed in the dashpot....the device that holds the doors closed (or partially closed), , proportional to engine vacuum (load), even though the air velocity is great enough to open the air doors. Opening up the bleed allows the vacuum to bleed off faster, and thus the air doors can open faster. The engineers that designed the Q jet were pretty smart !!
Next, I may fabricate a custom crank arm to enable easy changes to pick up point and total opening of the secondary valves, below the air door.
All the adjusting I referred to involves the "air door" at the top. If you pushed it open manually with engine off, you could feel a slight hang up ....but then it was fine. Both valves's outermost edge was binding ever so slightly on the top cover casting...IE the throat at, and around the secondary air doors. This was possible causing a slight delay. The big improvement was gained by opening up the bleed in the dashpot....the device that holds the doors closed (or partially closed), , proportional to engine vacuum (load), even though the air velocity is great enough to open the air doors. Opening up the bleed allows the vacuum to bleed off faster, and thus the air doors can open faster. The engineers that designed the Q jet were pretty smart !!
Next, I may fabricate a custom crank arm to enable easy changes to pick up point and total opening of the secondary valves, below the air door.
