Quadrajet Carb?

Question

I have a 1984 Oldsmobile with a V8 307 engine with a Quadrajet 4 barrel carb.. I just replaced the carb with a new one since the old carb was spewing gas out of the float vents. The car ran perfectly before this happened. But ever since the old one went bad and I put the replacement carb on it the engine runs rough. The directions say every adjustment is on factory settings. but I had to increase the idle and slightly adjust the Idle Mixture screws. I want to know where would the optium setting would be at. I heard its 4 1/2 turns after bottom out the idle mixture screws for a start. But how many turns is the factory Setting. I also checked the timing and the its off quite a bit the mark is pretty much in the 12 o'clock positition when it should be at 20 BTDC. which in my estimate its 10 to 15 Degrees off. the distributor was never touched when it was running fine or after the carb was replaced.

This New carb is also a QuadraJet remanufacture by champion. The old one was a Quadrajet made by Rochester.

Answer 1

http://i2.photobucket.com/albums/y22/tech30528/carbspec.gif

These are the initial idle adjustment screw settings for that car. It sounds like you may have hooked up the vacuum line for the vacuum advance to the wrong port on the carb, causing the timing to be too far advanced.

http://i2.photobucket.com/albums/y22/tech30528/oldsvac.gif

To set the timing on that car, disconnect and plug the vacuum advance hose at the distributor, and short the diagnostic connector under the dash.

http://i2.photobucket.com/albums/y22/tech30528/alcl.gif

Short terminals A and B. I use a paper clip. With the engine running, this will set the MC solenoid on the carb to a flat 30 degrees and disable spark control so you can set base timing. Set timing to 20 degrees BTDC at 1100 rpm in park. You may have to clear codes after you set the timing and remove the jumper. Pull the ECM fuse for 15 seconds, or just disconnect the battery.

If you short terminals A and B with the key on and engine off, the check engine light will flash trouble codes. It will flash 12 three times, then each stored code three times. It will finish by flashing 12 three times again.

Answer 2

Since you said the car ran ok before you changed the carb, I would start there. rebuilding the old Qjet is probably the best, cheapest and easiest thing you could do. I know you already bought the new one, but where did you get it, (Summit?) is it the right one for your car (jetted properly for your engine. most are not from the box. did you replace gaskets, fuel filters etc? as far as the timing goes check your procedure, I don't think it is as far off as you think, you may be doing something wrong. (unplug vaccuum advance?) ...etc. It would have ran pretty crappy if it was that far off. Also check your book for proper timing, shouldn't that be atound 8 degrees btc??at 1500 RPM with total advance around 20-25 degrees or so?? two guys garage just did a ignition timing show last weekend I think- maybe check it out.

Answer 3

don't mess with that timing until you get the carb straightened out, thats not your problem, you have to get the carb set properly first, you should have gotten directions on how to set the carb when you got it, read them, basically you turn both adjusting screws in all the way until they just bottom out and then back them each out 11/2 turns and start the car up and let it warm up and you should have a tachometer or a vaccum gauge hooked up to set the carb, if using the tach screw the adjusting screws one at a time in or out until you get the highest rpm reading on the tach and if using a vaccum gauge you have to hook the gauge to the vaccum port that has full vaccum all the time and do the same thing you did when using the tach except adjust for the highest vaccum reading on the gauge. After you get this done make sure your vaccum advance hose is hooked to the proper vaccum outlet on the carb where it only has vaccum when you give it gas and then set your idle for 1,000 rpm. and you should see a difference.

Answer 4

Take off 'distributor to carburettor' vacuum line and plug. No vacuum leaks. Even better, attach a vacuum gauge to carb (looking for highest vacuum) 3 1/2 turns to start. Then screw in one at a time until the engine idle begins to slow, then unscrew 1/3 turn. Adjust idle speed, then repeat mixture adjustment, readjust idle speed if necessary. You'll find this to be pretty close.

Answer 5

did you replace the carb with a q-jet or something else. if you can you should just find someone to rebuild the old carb. i thought replacing my q jet with a holley was a good idea. wrong my motor never ran right with an aftermarket carb. the rebuild kit is cheap and so is the rebuild if you can you should put an aftermarket intake manifold on there it gives the fuel better direction when it is in put into the cylinders good luck