Is tuning a quadrajet as easy as getting max vac and setting idle

[IT Cowboy]

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]

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]

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

[Badride76]

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]

Originally Posted by Badride76

What more is there to adjusting it?

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

[Dead Parrot]

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.

[IT Cowboy]

Again my vacuum reads 15 counted to the PCV valve port. The timing says it is right at 10 degrees so it might need some tweaking or that 15 vacuum might be normal for my setup

[cadillac_al]

Most of my engines pull around 18. The 350 in my K20 pulls 21. My GMC pulls 15 and I am kinda disappointed but it runs perfectly fine. I can't figure that one out but it does have 190k miles. Never had a 350 with that many miles. Back in the day a lot of carbs got rebuilt because of bad points. If you have points and haven't changed them yet then you need to.

[Dead Parrot]

Originally Posted by IT Cowboy

Again my vacuum reads 15 counted to the PCV valve port. The timing says it is right at 10 degrees so it might need some tweaking or that 15 vacuum might be normal for my setup

PCV port is a poor place to measure. Better to use the manifold port on the front of the carb and have the PCV valve hose in place.

Is that 10 degrees with the dizzy vacuum pot disconnected? Yes is the good answer.

18~20 inches is more normal for a stock cam with vacuum pot connected to manifold vacuum. Non stock cams often have less idle vacuum.