Is tuning a quadrajet as easy as getting max vac and setting idle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**IT Cowboy** · 02-18-2025, 06:11 PM

I just watched a video on how to do a basic tune on a quadrajet using a vacuum gauge. It shows that you set the front mix screws one at a time until you have max vacuum on the gauge and then set the idle screw to the desired rpm.

Is this something I can attempt without really messing something up? My truck seems to be running rich and smells like gas under the hood when running. I looked for leaks in all the normal places so I thought I would check the air/fuel mix adjustment vacuum first and then the timing.

https://www.youtube.com/watch?v=Nbih0zm_Ldw

GSP7 · Yesterday, 03:26 PM

There's more to it than that if you just installed a new rebuilt Qjet from someone else

I just finished a Qjet rebuild using Cliff Ruggles parts

Waiting for the weather to get better so I can do some intake manifold pressure wash cleaning and get to R&R'in. My shop is snowed in.

**IT Cowboy** · Yesterday, 04:16 PM

My vacuum gauge attached to the front pcv port is at 15 steady at idle if that says anything

Badride76 · Yesterday, 05:16 PM

Quote:

Originally Posted by GSP7

There's more to it than that if you just installed a new rebuilt Qjet from someone else

I just finished a Qjet rebuild using Cliff Ruggles parts

Waiting for the weather to get better so I can do some intake manifold pressure wash cleaning and get to R&R'in. My shop is snowed in.

What more is there to adjusting it?

GSP7 · Yesterday, 05:34 PM

Quote:

Originally Posted by Badride76

What more is there to adjusting it?

Go here for answers:
https://cliffshighperformance.com/si...orum/index.php

Dead Parrot · Yesterday, 07:12 PM

All that adjusting the idle mix screws does is adjust the idle mix. The idle speed screw sets the idle speed. Neither has anything to do with running down the road tuning.

Things you can do from the outside also include picking which accel pump hole to use and making sure the choke is set correctly as well as the fast idle speed.

IIRC, you can swap the rods and hanger for the back two secondary barrels.

You have to open it up to change the primary jets and rods which is where the main tuning effort happens.

Also, set timing first. For a stock SBC, start around 8~10 and increase until it gets hard to start hot. This may take several days as adjusting the dizzy while leaning over a hot motor is not a lot of fun.

02-18-2025, 06:11 PM	#1
IT Cowboy Senior Member Join Date: Jan 2025 Location: Clarkdale, Arizona in a van down by the river Posts: 205	Is tuning a quadrajet as easy as getting max vac and setting idle I just watched a video on how to do a basic tune on a quadrajet using a vacuum gauge. It shows that you set the front mix screws one at a time until you have max vacuum on the gauge and then set the idle screw to the desired rpm. Is this something I can attempt without really messing something up? My truck seems to be running rich and smells like gas under the hood when running. I looked for leaks in all the normal places so I thought I would check the air/fuel mix adjustment vacuum first and then the timing. https://www.youtube.com/watch?v=Nbih0zm_Ldw __________________ '72 C10 / 402 ___________________________________________ Freedom isn't safe, it requires you to take responsibility for your own life, your own safety, and your own success. It carries with it the possibility of failure and the understanding that you're working without out a safety net. If you give the state the responsibility for any of these you also give up the freedom that accompanies the responsibility.

Yesterday, 03:26 PM	#2
GSP7 Registered User Join Date: Sep 2012 Location: Idaho Posts: 751	Re: Is tuning a quadrajet as easy as getting max vac and setting idle There's more to it than that if you just installed a new rebuilt Qjet from someone else I just finished a Qjet rebuild using Cliff Ruggles parts Waiting for the weather to get better so I can do some intake manifold pressure wash cleaning and get to R&R'in. My shop is snowed in. __________________ '81 K20 Silverado , '99 Dodge Cummins 4x4, '05 Dodge Cummins 4x4, Pinstriping-Lettering-Specialty Painting Last edited by GSP7; Yesterday at 03:37 PM.

Yesterday, 04:16 PM	#3
IT Cowboy Senior Member Join Date: Jan 2025 Location: Clarkdale, Arizona in a van down by the river Posts: 205	Re: Is tuning a quadrajet as easy as getting max vac and setting idle My vacuum gauge attached to the front pcv port is at 15 steady at idle if that says anything __________________ '72 C10 / 402 ___________________________________________ Freedom isn't safe, it requires you to take responsibility for your own life, your own safety, and your own success. It carries with it the possibility of failure and the understanding that you're working without out a safety net. If you give the state the responsibility for any of these you also give up the freedom that accompanies the responsibility.

Yesterday, 07:12 PM	#6
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,645	Re: Is tuning a quadrajet as easy as getting max vac and setting idle All that adjusting the idle mix screws does is adjust the idle mix. The idle speed screw sets the idle speed. Neither has anything to do with running down the road tuning. Things you can do from the outside also include picking which accel pump hole to use and making sure the choke is set correctly as well as the fast idle speed. IIRC, you can swap the rods and hanger for the back two secondary barrels. You have to open it up to change the primary jets and rods which is where the main tuning effort happens. Also, set timing first. For a stock SBC, start around 8~10 and increase until it gets hard to start hot. This may take several days as adjusting the dizzy while leaning over a hot motor is not a lot of fun.



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