Q-Jet help - "power piston spring"
Thread Starter
Pro
Joined: Oct 2000
Posts: 509
Likes: 0
Q-Jet help - "power piston spring"
I'm following Lars's guide to getting my Q-Jet tweaked (great guide, someone needs to pay this guy!), and I've traced my "non-responsive" idle mixture screws problem and rich condition at idle problem down to the fact that my power piston spring is too stiff. My engine only develops about 13.5" of vacuum at idle, so the spring apparently keeps the power piston raised, raising the rods in the jets and allowing too much fuel to pass through the primary jets etc. I removed the spring, and now it idles like a dream and doesn't smell at all "gassy". Really woke up the off idle response too. NOW....My question:
How can I make this spring "softer"? Or, are softer springs sold? The usuals do not list them (Jegs, Summit), or I'm looking in the wrong places. I either want to make is softer or buy a softer spring. Any suggestions?
How can I make this spring "softer"? Or, are softer springs sold? The usuals do not list them (Jegs, Summit), or I'm looking in the wrong places. I either want to make is softer or buy a softer spring. Any suggestions?
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
I got the Edelbrock spring set from summit, part number EDL-1994.
Four springs for super-tuning your Quadrajet.
Power Piston Spring Assortment, 4 Pack
These Edelbrock Quadrajet Power Piston spring kits include four different color-coded springs that will help you fine-tune your Quadrajet carburetor for varying loads and conditions.
Kit contains:
* One 4 in. Hg gold spring
* One 5 in. Hg orange spring
* One 6 in. Hg black spring
* One 8 in. Hg yellow spring
Also you could try here:
http://www.carburetion.com/quadrajet.asp
Four springs for super-tuning your Quadrajet.
Power Piston Spring Assortment, 4 Pack
These Edelbrock Quadrajet Power Piston spring kits include four different color-coded springs that will help you fine-tune your Quadrajet carburetor for varying loads and conditions.
Kit contains:
* One 4 in. Hg gold spring
* One 5 in. Hg orange spring
* One 6 in. Hg black spring
* One 8 in. Hg yellow spring
Also you could try here:
http://www.carburetion.com/quadrajet.asp
Pro
Joined: Nov 2001
Posts: 684
Likes: 0
From: Winnipeg Manitoba
Is it possible that you had the incorrect spring for your carb. I have thought about the spring on my carb, but I am unsure how to determine whether the spring in there is the correct one. Is there a way to determine this and with the Edel spring kit, how does each spring change your carbs operation ? Thanks
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
RAT -
I see quite a few Q-Jets that have been modified with some very creative power piston springs: I've had carbs sent to me with ball point pen springs, stretched springs, cut springs, and no springs.
There's no good way to determine if a spring you pull out is the correct, or original, spring. If you look at my Q-Jet Listing Chart, I list all the part numbers for the correct springs. I have purchased all the available spring part numbers from GM, and I use these springs as "reference" springs when I build carbs: I simply pull the spring out of the carb and visually compare it side-by-side to one of my correct part number springs. This is the only way I know to do a quick check.
Swapping springs changes carb operation by altering the enrichment point. If enrichment occurs too soon (stiff spring), the carb will operate in the power enrichment mode prematurely, often affecting idle quality and cruise performance.
I see quite a few Q-Jets that have been modified with some very creative power piston springs: I've had carbs sent to me with ball point pen springs, stretched springs, cut springs, and no springs.
There's no good way to determine if a spring you pull out is the correct, or original, spring. If you look at my Q-Jet Listing Chart, I list all the part numbers for the correct springs. I have purchased all the available spring part numbers from GM, and I use these springs as "reference" springs when I build carbs: I simply pull the spring out of the carb and visually compare it side-by-side to one of my correct part number springs. This is the only way I know to do a quick check.
Swapping springs changes carb operation by altering the enrichment point. If enrichment occurs too soon (stiff spring), the carb will operate in the power enrichment mode prematurely, often affecting idle quality and cruise performance.
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
Let me see if I can remember this correctly...
You can check the power piston spring action by gently probing (I used a balsa stick) down the orifice tube. First, check the power piston action when the engine is off. You should be able to press it down, and the spring will push it back up. Next, check it at idle. The spring should be held down as a result of the engine vacuum. If the spring is too strong, it will hold the piston up at idle -- not good. If the spring is too weak, the piston will not be lifted up during accleration. As you accelerate, the resulting vacuum drop allows the spring to push the piston up, thus richening the mixture.
(I was writing this at the same time as Lars. Did I get it right, Lars?)
You can check the power piston spring action by gently probing (I used a balsa stick) down the orifice tube. First, check the power piston action when the engine is off. You should be able to press it down, and the spring will push it back up. Next, check it at idle. The spring should be held down as a result of the engine vacuum. If the spring is too strong, it will hold the piston up at idle -- not good. If the spring is too weak, the piston will not be lifted up during accleration. As you accelerate, the resulting vacuum drop allows the spring to push the piston up, thus richening the mixture.
(I was writing this at the same time as Lars. Did I get it right, Lars?)
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Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by page62
Did I get it right, Lars?
You can stick anything down the vent tube to hit the power piston, like a long pin punch, skinny screwdriver, etc., but you have to be careful: I've seen people stick things right through the float doing this... so the wooden stick is a good idea. I use a pin punch, but I'm very careful to stick it down gently and "feel" for the piston so I don't damage the float.
