Rochester Quadrajet Tuning....
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
Rochester Quadrajet Tuning....
I want to adjust the "Adjustable Part Throttle" APT screw in this quadrajet carb I have. I got it out using needle nose, but now I want to be able to set the primary needles to the correct height....and needle nose are just not going to do it.
I APT screw head is a rectangle, 1/16" x 1/8"...I have tried to find some tubing to form into a rectangle, but so far no go on that.
Is there a "tool" available? I have yet to find one.
Thanks,
LannyL81
I APT screw head is a rectangle, 1/16" x 1/8"...I have tried to find some tubing to form into a rectangle, but so far no go on that.
Is there a "tool" available? I have yet to find one.
Thanks,
LannyL81
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
I did a basic search on Google and found several sites. This one seems to have a lot of stuff so they may be good to start with for info and availability.
http://www.thecarburetorshop.com/Rochester_tools.htm
http://www.thecarburetorshop.com/Rochester_tools.htm
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
Are you saying you used a 1/4" x 20 bolt? If so do not see how that would work as the one I took out is at best about a #6 screw.
I guess I could try a #6 screw with a nut in the same location as this shoulder piece that is on the original APT screw and grind the screw head down in diameter so it will fit into the "tube" in the carb. I'll have to give that a try as I am getting nowhere with finding a 1/16" x 1/8" rectangle bit / driver.
Thanks.....
I guess I could try a #6 screw with a nut in the same location as this shoulder piece that is on the original APT screw and grind the screw head down in diameter so it will fit into the "tube" in the carb. I'll have to give that a try as I am getting nowhere with finding a 1/16" x 1/8" rectangle bit / driver.
Thanks.....
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Are you saying you used a 1/4" x 20 bolt? If so do not see how that would work as the one I took out is at best about a #6 screw.
I guess I could try a #6 screw with a nut in the same location as this shoulder piece that is on the original APT screw and grind the screw head down in diameter so it will fit into the "tube" in the carb. I'll have to give that a try as I am getting nowhere with finding a 1/16" x 1/8" rectangle bit / driver.
Thanks.....
I guess I could try a #6 screw with a nut in the same location as this shoulder piece that is on the original APT screw and grind the screw head down in diameter so it will fit into the "tube" in the carb. I'll have to give that a try as I am getting nowhere with finding a 1/16" x 1/8" rectangle bit / driver.
Thanks.....
Keep the shiny side up!
Scott
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Here is a pic of the adjustment tool. The slot in the head matches the slot in the bottom, so you know how much you are turning it. Either 5/16 or 3/8" bolt. Don't remember, would have to measure it.
The alum plug is knocked out and a stainless socket hex plug is threaded in to replace the plug.
Here is the ss plug, it has to be flush or lower for the air cleaner.
The alum plug is knocked out and a stainless socket hex plug is threaded in to replace the plug.
Here is the ss plug, it has to be flush or lower for the air cleaner.
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Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
:rof l:NOW....that makes sense.....yes it is a good laugh....
I totally, completely misunderstood the 1/4 bolt......wow...must have had my brain turned off or something.
Thank you....and a big....DUH from me.....
Excuse me now....I have to go do some brain surgery.....
Last edited by LannyL81; Feb 22, 2012 at 02:09 PM.
Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
OK, now that you have the tool, what procedure are you going to use to adjust it to the proper setting. The only thing I found required the carb to be taken apart. I just played with mine until it ran OK but I would like to know if there is a spec that I can set it to.
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
It's kinda like the idle screws, there is no spec, you just play with it till you get it where you want it. I suggest that you bottom it out from where it is now, counting how many turns it takes then bring it back up and begin tuning. That way you will have a baseline adjustment, if it gets all screwed up, you can start from scratch at the baseline adjustment.
Keep the shiny side up!
Scott
Keep the shiny side up!
Scott
Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
It's kinda like the idle screws, there is no spec, you just play with it till you get it where you want it. I suggest that you bottom it out from where it is now, counting how many turns it takes then bring it back up and begin tuning. That way you will have a baseline adjustment, if it gets all screwed up, you can start from scratch at the baseline adjustment.
Keep the shiny side up!
Scott
Keep the shiny side up!
Scott
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
my technique
If light tip-in is soft, back it out 1/4 turn. It is a very sensitive setting and optimum may vary for cold vs hot weather.
This was before the widebands were available.
Last edited by Rich's'78; Feb 22, 2012 at 12:53 PM.
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
I know that putting the APT screw all the way down is full lean, so I had planned on going one full turn to start with and then go from there.
I do not have a wide band O2 sensor to use so will be tuning by trial and error. Same goes with the idle mixture screws.
I do not have a wide band O2 sensor to use so will be tuning by trial and error. Same goes with the idle mixture screws.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Running Proceedure
Turn APT clockwise (leaner) 1/4 to 1/2 turn at a time until surging at steady throttle is felt at steady highway cruising speeds.
Then turn up until surging stops.
Idle screws usually anywhere from 3 to 6 turn out.
Turn APT clockwise (leaner) 1/4 to 1/2 turn at a time until surging at steady throttle is felt at steady highway cruising speeds.
Then turn up until surging stops.
Idle screws usually anywhere from 3 to 6 turn out.
