Rejetting for power?
 

Hey guys, I have a 1985 Pontiac Trans Am WS6, and it has the LG4 engine and t-5 transmission. I recently put a set of hooker headers on and plan to get a new camshaft within the next few months with upgraded valve springs. I was wondering if rejetting my quadrajet a bit richer would help with driveability/power, seeing as whenever I start the car until I've driven it for a bit it stumbles on its face whenever more than 65-70 percent throttle is given. Knowing that this engine was designed for fuel economy (which I am not getting:)), would running a little richer be a good way to go with more airflow in and out of the engine? Thank you.

Re: Rejetting for power?
 

The electronic qjet will self adjust the mixture for the primaries fine. Provided it's functioning correctly and the dwell has been set correctly you should be good.

A change in secondary rods and hanger is usually a good thing though. There's a tech article here somewhere.

Re: Rejetting for power?
 

I find that most carbs are running way too rich.

Re: Rejetting for power?
 

The best thing you can do is install a wide band O2 sensor. That will answer all of your questions.

Re: Rejetting for power?
 

That's what I did. Makes tuning a breeze.
A vacuum gauge and a wide band O2 and almost over night you are now a carb tuning master.
With a vac gauge and wide band gauge every little pop or stumble is explained, those 2 pieces of instrumentation remove about 98% of the guess work from tuning a carb.

Re: Rejetting for power?
 

I've taken it a step further and also have an Innovate LM-1 data logger. I've added a MAP sensor and can monitor RPMs, AFRs and engine load. Lots of interesting data collected and it really helps with the tuning process. I've a Barry Grant vacuum secondary carb that's been modified for greater adjustability too. High and low speed air bleeds as well as the idle circuit air bleed now all have screw in jets.

Re: Rejetting for power?
 

Rejetting may worsen the situation depending on where you're at now. That's why a wide band is so important. If your fuel economy sucks with a QJet, then chances are you're much too rich at part throttle. The stumble you experience at part throttle tip in could be attributed to the air valve being improperly adjusted.
You could very easily be rich in one range of operation and lean in another. Those with more experience with the QJet may have better insights (my tuning with them is very dated as I haven't run one in decades) but whatever the situation, you're really flying blind without an AFR gauge.

Re: Rejetting for power?
 

correct me if I'm wrong but the o2 sensor I just replaced when I installed my headers was a narrowband and only reads lean and rich. So, if down the road I get a wideband (seeing as they aren't very cheap) I would have to have a bung welded into perhaps the passenger side header collector or maybe further upstream of my current one? Is it possible to replace the narrowband with a wideband and still keep the computer happy and maybe run a gauge into the passenger compartment? I'm not super techy when it comes to wiring, (I wired up a tach, only took me about 6 hours and way too many zip ties)

additionally, I have always had a cel on, except for occasionally when there is a cold start and it kicks onto the far high idle. One time while I was trying to figure it out I wiggled the kinda gacked connection for the choke heater relay and it jumped onto high idle and the cel went away. Not sure if this is relevant, thanks.

Re: Rejetting for power?
 

The LG4 ECM will not be able to read the wide band O2

Re: Rejetting for power?
 

The oxygen sensor plugs into the gauge, the gauge needs an ignition on +12v source and a ground. All you have to do is figure out where to get the key switched 12v power and run the wires.

Re: Rejetting for power?
 

Ok, when I found a guy to help me weld up a y pipe, (which believe it or not gave me significant butt dyno gains and now seems to rev much much easier at higher rpm like 5000-5300) he said it was clearly running crazy rich. When I bring it back to have a hole in the floorboard patched he said he would fix my carb, check the vacuum advance, and maybe do a compression test. He is a Quadrajet guru, and knows them inside and out. The quadrajet on my LG4 is a 750cfm unit, correct?

Re: Rejetting for power?
 

Don't expect too much of this GURU. Your LG4 does not use vacuum advance (which someone with some experience should know).