Quadrajet Questions
Thread Starter
Drifting
Joined: Mar 2013
Posts: 1,926
Likes: 304
From: Lansing MI
Quadrajet Questions
Alright so I decided I would give my 75s qjet a rebuild and attempt to fix Bubba's zip tied choke job and the **** poor starting and idling. I picked up a rebuild kit and ordered an electric choke conversion kit.
Some before pictures
Attachment 48363400
Attachment 48363401
Attachment 48363402
Disassembled
Attachment 48363403
Cleaned up and rebuilt minus the new choke because I didn't have the right tap to thread the holes
Attachment 48363404
That brings me up to last night. I installed the carb onto the car and it fired right up without having to crank and crank like I used to have to do. It was quite refreshing to turn the key and have it fire right up without having to feather the gas for 10 minutes. The issue now is that it is idling too high now. With the idling adjustment all the way down I'm idling at about 1200 rpm. Pictures below show this.
I'm trying to figure out the high idle. Someone mentioned a possible vacuum leak. I used a guage and I was holding a steady 17 on the guage. I did feel a vacuum pull at the front of the carb. In the picture below there is an arrow pointing to where the vacuum pull was at. I do not have a tube at this spot, only a hole. Is this normal?
My other thought is that the timing may just be off. Any input would be appreciated.
Some before pictures
Attachment 48363400
Attachment 48363401
Attachment 48363402
Disassembled
Attachment 48363403
Cleaned up and rebuilt minus the new choke because I didn't have the right tap to thread the holes
Attachment 48363404
That brings me up to last night. I installed the carb onto the car and it fired right up without having to crank and crank like I used to have to do. It was quite refreshing to turn the key and have it fire right up without having to feather the gas for 10 minutes. The issue now is that it is idling too high now. With the idling adjustment all the way down I'm idling at about 1200 rpm. Pictures below show this.
I'm trying to figure out the high idle. Someone mentioned a possible vacuum leak. I used a guage and I was holding a steady 17 on the guage. I did feel a vacuum pull at the front of the carb. In the picture below there is an arrow pointing to where the vacuum pull was at. I do not have a tube at this spot, only a hole. Is this normal?
My other thought is that the timing may just be off. Any input would be appreciated.
Pro
Joined: Mar 2015
Posts: 681
Likes: 31
From: Nebraska
The hole needs to be plugged, that's one thing. The throttle not closing all the way could be caused by the primary throttle plates not centered in the bores. Loosen the screws a bit, close the throttle...they will center themselves. Hope this helps.
Le Mans Master
Joined: Oct 2007
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From: Akron Ohio
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Where did you set your idle mixture screws? You should lightly screw them in until they seat, and then back off 1.5-2 turns. Screw each one in just a little (like 1/8-1/4 turn at a time) until you get the highest vacuum reading, right before killing the engine. Then set your idle down to where it will go.
Thread Starter
Drifting
Joined: Mar 2013
Posts: 1,926
Likes: 304
From: Lansing MI
Where did you set your idle mixture screws? You should lightly screw them in until they seat, and then back off 1.5-2 turns. Screw each one in just a little (like 1/8-1/4 turn at a time) until you get the highest vacuum reading, right before killing the engine. Then set your idle down to where it will go.
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Wow, that thing was a mess before. The EGR valve was hooked up to the choke! Quite something. The original hot air choke is supposed to be hooked up to a line that connects where there's a rectangular void in the intake on the passenger side on your car. Is this still open? Post pictures of both sides of how the carb looks now.
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Thread Starter
Drifting
Joined: Mar 2013
Posts: 1,926
Likes: 304
From: Lansing MI
Wow, that thing was a mess before. The EGR valve was hooked up to the choke! Quite something. The original hot air choke is supposed to be hooked up to a line that connects where there's a rectangular void in the intake on the passenger side on your car. Is this still open? Post pictures of both sides of how the carb looks now.
I'm out at the garage dialing things in today. I readjusted the idle mixture screw, the choke and the fast idle screw and got the idle dialed in right around 750.much lower and she wants to die.
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Yeah bubba did some work under there huh. I have a block off plate for the hot air choke and the egr valve at my house. They will be installed soon.
I'm out at the garage dialing things in today. I readjusted the idle mixture screw, the choke and the fast idle screw and got the idle dialed in right around 750.much lower and she wants to die.
I'm out at the garage dialing things in today. I readjusted the idle mixture screw, the choke and the fast idle screw and got the idle dialed in right around 750.much lower and she wants to die.
Thread Starter
Drifting
Joined: Mar 2013
Posts: 1,926
Likes: 304
From: Lansing MI
I'd bet on vacuum leaks from several spots. That hot air port is one if not blocked off, and any unused vacuum ports without plugs will also draw a considerable amount of air. There's also a small tube between the choke housing and the body of the carb that can be a vacuum leak source.
Thanks for the pointers everyone.
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Vacuum leaks could have been causing the high idles issues from yesterday. I taped over that hot air port as a temporary fix to adjust everything until I can get a plug for that hole. The tube between the choke housing and carb body shouldnt be too big of an issue because I switched the choke housing over to the later one for electric chokes.
Thanks for the pointers everyone.
Thanks for the pointers everyone.
Check all over for vacuum leaks and eliminate them all, and then have another look at your mixture and idle speed screws.
Last edited by Brcmpbl; Mar 29, 2016 at 09:28 PM.
Thread Starter
Drifting
Joined: Mar 2013
Posts: 1,926
Likes: 304
From: Lansing MI
Wow, that thing was a mess before. The EGR valve was hooked up to the choke! Quite something. The original hot air choke is supposed to be hooked up to a line that connects where there's a rectangular void in the intake on the passenger side on your car. Is this still open? Post pictures of both sides of how the carb looks now.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
The throttle blade is not closing all the way. I suspect the choke linkage is either hung up, or you have the new electric choke set way too tight. Try holding the choke flap all the way vertical and flicking the throttle blade.
Have you got your electric choke wired in so that it heats up and opens the choke yet?
Have you got your electric choke wired in so that it heats up and opens the choke yet?
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Also, there's only one hole in the choke system that pulls a vacuum - the one between the carb body and the choke housing itself. This one should use be plugged with RTV or epoxy to prevent vacuum transfer. If it isn't, though, it's a very small vacuum leak, not enough to cause a 600RPM delta.
Race Director
Joined: Apr 2003
Posts: 19,350
Likes: 654
From: Tampa, Florida
As others have noted are you sure it's off the fast idle cam? How's you timing? A change in timing could drop the idle speed which in turn will allow you to turn the idle screw in.
I believe Lars recommends starting at 4 turns out on mixture screws.
I believe Lars recommends starting at 4 turns out on mixture screws.