hello everyone! You all really helped me out with my '89 305 TBI, so I've come back with a question about my 1980 Z28 350 with non-computer-controlled Quadrajet. The second gen forum I'm on really isn't replying at all.

anyways, the car runs way to rich. Black smoke comes out when you stomp on it (especially when warm), it gets a maximum of 11 mpg, and sometimes it hesitates when you stomp on it. Other than that it runs great...really smooth idle.

So I'm thinking I should reset the timing and the carb adjustment.

So in order to set the timing, do I have to plug up the vacuum port on the distributer? Should I set the carb first?

As far as the Carb goes...the last time we set it we had to turn the screws out like 10 turns before the RPMs stopped rising! Is this normal? it's a rebuilt one from Holley with the exact same model number as my old one. when we set the old one we had to do the same thing.

How many turns would be a safe setting to start out at when adjusting the carb? my dad did it last time, but now I'm on my own and don't wanna mess things up.

OH YEAH ALL THE EMISSIONS STUFF (EGR, CAT, SMOG) IS GONE...DOES THIS MAKE A DIFFERENCE FOR CARB AND TIMING SETTING?

I'm starting to drive the car again, and I just want it to be a little more fuel efficient and for the smoking to stop! It's kind of embarrassing sometimes!

Thanks for reading all this and I hope you can help!

 

Your setup is probably using timed vacuum, so it won't matter if you disconnect the vacuum port on the distributor or not when you set the idle timing. Set the distributor up as described in the tech article here.

Emissions-era carbs use long-tapered idle mixture screws so they're a lot less sensitive. It can take a lot of turns to make any change.

There aren't any "unsafe" settings. As long as it runs, you can tune from there.

Not so much. The EGR can make some difference to the part-throttle vacuum advance settings.

 

Try hooking up your distributor to manifold vacuum after you do the initial timing adjustment. The timing will jump way up at idle once its hooked up there, but it should help low rpm driveability and economy out somewhat, and will probably run smoother too (at least, all that is true in my case). If you try this, the idle speed will probably jump way up, so you'll have to drop it down to where it was with the idle speed screw.

Also, make sure the choke is opening all the way. Sometimes the linkage can get all full of junk just from normal driving, and cause it to stick before its all the way open, which will make it run somewhat rich. If the linkage looks dirty, spray it out with some throttle body cleaner (same as carb cleaner, but less oil in it for dirt to stick to).

To set the idle mixture screws, you really should have a vacuum guage. Hook up the vacuum guage to manifold vacuum, start it and let it run and get warm enough that the choke is open all the way and it idles fine on its own. Now what you want to do is close the idle screws (turn them in) about 1/4 turn at a time, doing each screw the same amount (1/4 on left, then on right, etc) untill you see the vacuum level start to drop off. When you see it drop off a bit, turn it back out about 1/4 turn on each side and you should be set now.

If your Qjet has the really fine-thread idle screws (and it should if its an '80 correct Qjet), change "1/4 turn" above into "1/2 turn" and you should be good.