Q-Jet Tuning

by 76 Malibu Thu Jul 04, 2024 11:17 pm

I am working on fine tuning my Q-Jet on my car. It is not original to the car. The specs are as follows:

Cab #: 17082283
Prim Jets: 76
Prim Rods: 44B
Secondary Rods: CH

The carb was rebuilt with a Cliff's High performance kit and speced out by Cliff Ruggles.

I got the primaries pretty dialed in. This car seems to cruise well at a leaner mixture, and have settled at about 15:1 to 16:1 for light cruise (varies depending on speed an load). There is no surge or any other issues. It actually seemed to cruise okay at even leaner mixtures, as much as 17:1, but I didn't want to go too lean. Idle is set to about 13.5:1, as it seemed to like a richer idle (it would surge if much leaner).

My issue is that when I get into the throttle deeper or got to WOT, my mixture is rich, high 11s, low 12s. It also seems somewhat sluggish, like a rich bog. At lower throttle inputs it is very responsive and feels great. Any advice on leaning out the secondary side short of swapping rods?

by zucchi Mon Jul 08, 2024 8:12 am

Kinda wondering why you're reluctant to going with bigger rods?
Anyway, reducing the tension on the secondary air valve spring will cause the valve to open sooner and may lean it out.

by bracketchev1221 Mon Jul 08, 2024 8:28 am

Thats what I was wondering, if it can't get the air to go with the fuel and it goes rich. If you stay in it longer does it clear up at all or just stay rich?

by 76 Malibu Mon Jul 08, 2024 10:04 pm

It's not that I am opposed to changing the secondary rods, I just don't have any spares. I just wanted to make sure there was not something else I could do to fine tune the secondaries.The CH rods aren't too aggressive, so I am wondering if I need to look at a different hanger. The car runs so awesome at part throttle, but seems so sluggish at WOT. I know it's a smogger 350, but I think I can get it to pull better.

I have played with the air door tension but haven't noticed a big difference. If the air door opens faster won't that enrich the carb? The secondary air door controls the secondary rods. So if the door is not opened the rods are fully inserted into the jets. As it opens it pulls the rods out of the jets. Unless I am missing something?

by 73ss Tue Jul 09, 2024 7:01 pm

Air door does not effect mixture. Weight, gearing, engine, etc determine air door settings. The spring & pull off effect the opening rate. Loosen until you feel a bog when mashing the throttle, then tighten about 1/8 turn until bog goes away.

Rods & hanger control mixture. You can try a hanger with lower holes that places the rods deeper into the jets.

My AFR is 12.7 on WOT. Seems to like it there.

by 76 Malibu Wed Jul 10, 2024 4:15 pm

Thank you. I think I will start with a different hanger and see if I can fine tune that way then. I think I have an olds parts Q-jet in my garage, I will have to dig it out and check which hanger it uses. Otherwise, I will see what I can get from Cliff.

by TW Monte Fri Jul 26, 2024 1:02 pm

Also seems like there are different secondary cams that can be used to alter the amount of lift on the rods

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