basiccamaro

I got my plain-Jane, smog dog 1983 Berlinetta that has a 305 with the electronicaly controlled Quadrajet for a pretty low price. It's got a really straight body but I got it cheap because the previous owner could not keep it running, we towed it to my house after I bought it. The seller did not know very much about cars and had spent a TON of money at the local dealership trying to get it fixed. He spent a LOT of money on electric choke repairs, but the car was totally flooded out.

After I got it home I changed the plugs, put in a new coolant temperature sensor and disconnected the wire going to the electric choke assembly and wired the choke plate full open. I've been driving it that way since early spring and it has been very reliable. But even in warm weather the lack of a choke is a pain in the rear. After running long enough to warm up, everything runs pretty well. But now with cold weather coming on I'd like to get my choke working properly.

So can anyone describe all of the choke function and voltage flow? I checked for 12V on the electric choke wire and it does light up a test light, but the choke does not pull off correctly. Is there supposed to be a steady 12V (or other amount of voltage) on the choke wire at all times? Am I correct to think that the 12V building up resistance and heat in the choke coil pulls the choke plate off and keeps it off? And that when you shut the ignition off 12V drops at the wire and the choke coil cools off and makes the choke plate close? It seems pretty simple, but the car will flood out if I hook the wire up to the terminal on the choke housing. That's with voltage, and a brand new (courtesy of big money spent at the dealership by the PO) choke assembly. The choke plate also seems to move freely in the air horn.

Also, the car has what seems to be a problem getting fuel to the engine on a cold start up. I don't think that this is caused by the choke problem because it has the same problem in very hot weather too. I have to spin the engine over, stop, pump the hell out of the gas pedal, then re-crank the engine and then it will start and run fine. It does not stall out, sputter while running, it pulls hard (as hard as a low hp smogger 305 can pull) on accelleration and generally runs like it's getting plenty of fuel, except at first startup.
Is there anything else to check beside the in-tank fuel pickup, the filter on the Quadrajet, and is there an in-line fuel filter somewhere on the frame rail or uni-body structure? anything else to check? Thanks!

Damon

To answer your primary question, yes, the choke is supposed to get a full 12V any time the engine is running. It's got basically a little electrical heating element inside it that slowly over time (several minutes) heats the bi-metal spring inside, causing it to relax and open the choke. A quickie test of the choke element is to measure resistance from the terminal to ground (body of the carb) with everything at about room temerpature (not warmed up from running). A brand-new choke element will have about 10 ohms resistance. An old but passable choke can get as high as about 20 ohms. Anything over about 25 ohms and it's shot.

In a cc-QJet the choke element usually has a square notch in it's edge that lines up with a square indexing tit on the choke housing. As such, it's designed to be non-adjustable. Just hook it up to the arm inside the housing, turn to line up the squares so it can drop all the way home, tighten down the 3 screws and that's where it sits. Not all QJets have this "feature". Some you have no positive indexing system so you have to play with the rotation of the choke element to get the tension on the choke linkage right for cold starting. Moving on.....

Now on an overnight-cold engine the choke plate should snap closed as soon as you open the throttle to unload the choke linkage and allow it to move.

Now here's an important part.... AS SOON AS THE ENGINE FIRES the little vacuum canister on the front/pass. side of the carb should retract fully (it's hooked to a full vacuum port on the carb through a short piece of vacuum hose). There is a plastic piece on the arm of this vacuum canister that reaches down and FORCES the choke linkage to open the choke plate slightly- opens it about an 1/8" or so at the choke plate. This is important for preventing the engine from immediately flooding out on startup. You can't have the choke plate fully closed on a running engine so this little vacuum can is what pops it open slightly to prevent flooding. There is an adjustment screw on the arm to adjust how far it opens the choke plate when it retracts. So the proper functioning of this vacuum canister is important (a simple check is to see if it holds vacuum and the arm goes in and out when you apply/remove vacuum).

After that point, slowly, over a period of minutes the choke should heat up and gradually open the choke plate on it's own until it reaches the point where it's fully open (vertical).

Last critical piece in the choke system is the fast idle cam. Built into the choke linkage is a step cam and follower (down low, by the primary throttle shaft). This provides for a higher idle speed any time the choke is closed. The further it's closed the higher the idle speed. When the choke gets fully opened it drops off the last step of the fast idle cam and idle speed adjustment is then left up to the regular old curb idle speed screw on the driver's side of the carb that I'm sure you are familiar with (and is not dependent on the choke system).

Like the vacuum canister, there is an adjustment screw built into this linkage so you can control how much the fast idle cam system affects cold idling speed. You can see the head of the adjustment screw way down under the choke linkage, pointing forward, any time the choke is fully closed. A good starting point would be to have the idle settle in around 1200-1300 RPMs immediately after starting overnight-cold. You don't want it too low because carbed engines don't like idling real low when they're cold, but you also don't want the engine racing either- makes dropping into gear rather harsh.

Make sure all this stuff is FUNCTIONAL, then you can tune the adjustments to dial it in. You really only get a couple shots at it every morning beore things get too warm and the adjustments become meaningless.

ternandes

iTrader: (7)

My man Damon is right on the money. Great job of explaining the whole choke system, which seems to confuse a lot of people. Even when they were more or less standard on all cars, most mechanics did not understand carbs and chokes very well. I wish I had a dollar for every guy I knew back then who would put in a manual choke because he couldn't figure out how the automatic choke worked.

Zwrench

I agree. That is a very good description of choke operation!

Some QJs have a problem with fuel draining from the float bowl after sitting a few hours (i.e. overnight). It causes hard starting because it takes a bit of cranking for the fuel pump to refill the bowl. I'm attaching a picture of a service bulletin that describes the problem and the fix. It's from 1973 but, QJs had the same problem in the 80s as well. I don't know if the seal in the bulletin (p/n 7041342) is still available but, I'll tell you how I used to fix them.

Take the carb off of the engine and drain the gas from it. Flip it over and remove the throttle body. In the center of the bottom of the float bowl you'll see two aluminum plugs. Clean those up real good and coat them with two-part epoxy. Don't use too much as it can hit the bottom of the throttle body assembly and cause binding. Let it harden overnight. Before reassembly, check your carburetor base gasket and throttle to bowl gasket for any sort of damage and replace as needed.

Before you do that however, check fuel pump pressure and volume, filters and lines. Start with the simple stuff.

basiccamaro

Guys, thanks for the AWESOME replies to my post! I'm going to both save them to a file and print them off.



When I got this car I got the repair bill receipts from the PO's trips to the Chevy dealership(several visits) and you just would not believe how much money he spent at the dealership and still ended up selling the car very cheaply, and not running. Some of the expense was also for brand new exhaust manifold air pump tubing that wasn't even screwed into the manifold at several ports! Unbelievable, at least I know wht dealership to NEVER take my car to for service, even though I try to avoid that whenever possible anyway.

Late last night after posting my original questions, I had a thought. With the thick Quadrajet-to-intake manifold gasket, does the carb body ground well enough to the intake manifold? Would the carb bolts be a good enough ground path?

And I am also a Q-Jet lover. I just rebuilt one for a 1986 454 Suburban using Ruggles' book and parts to learn more about how to do it better. I am really happy with the results. They give good fuel economy when driving only on the primaries and can still support big horsepower on the top end, especially after being rebuilt to proper specs and modified for better performance.

Zwrench

Yes, the bolts and the fuel line are ample ground paths. There's no concern there.