I bought a Quadrajet carburetor from Cliff Ruggles two years ago. Took some time until my restoration has progressed so far that I could install this carb. It is a 1968 original Pontiac carburetor. The number is 7028265, 750cfm, divorced choke. Originally it was meant for a manual transmission, non Ram Air, but Cliff made some minor internal modifications to run it on my 68 400 Firebird with AT TH400. Everytime I drive the Bird it is nearly perfect - the only problems I got (and still get) is when standing in a traffic jam or at a stop light: the car´s nearly dying at low idle... In fact it never did but mainly because I always stepped on the accelerator pad (pressing the brakes at the same time or pressing the accelerator after switching into neutral gear). It´s the same when I stand at a stop light and switch into neutral gear immediately after stopping. It´s NOT every time but it doesn´t change with cold or warm engine. As soon as I stop at a stop light I´m getting nervous because I wait for the engine first running unsteady, then nearly dying. As soon as I drive -- no problem at all! And even if I park the car and keep the engine´s running for 20 minutes sometimes it runs without any flaws. So I never know when to expect problems. Everything´s completely new and rebuilt on this car: it has new fuel lines, new fuel sender, new fuel pump, new filters, completely redone engine - everything you could imagine. I followed Cliff´s advice and run a correct stock (new) fuel pump to make sure it does not put out over about 6 psi pressure. I run 100 octane fuel (it´s the highest grade fuel available in Germany) with additional fuel additive for ensuring best internal lubrication.
Okay, so far my issues...
There are not a lot of people around here who know how to fine tune a 4bbl carb so I sent an email to Cliff Ruggles. He replied immediately:
Quote:
Couple of things to check. Lubricate the primay and secondary throttle shafts with light oil, and work the linkage a few dozen times, to make sure that the throttle plates are fully seating.
With the engine fully warmed up, set the idle mixture screws for the best idle quality.
You can also remove the triangular cover over the upper idle airbleed screw, for fine tuning. It may help to add a small amount of idle air to lean it up some. The mixture screws should end up about 1.5 to 2.5 turns out from seated. Once you find the ideal settings, it should idle stable in and out of gear every time you stop.
Let me know how it works?.....thanks....Cliff
Cliffs High Performance 20579 Berry Road Mount Vernon, Ohio 43050 740-397-2921
Ouh, yes. That´s about the same as explaining colours to a blind man...
I posted some pics of my carb below. Can anybody please explain what screws I should turn and how I can avoid to completely mix up my carb?? Any help would be appreciated; I never ever worked on a carb before... I´m sure Cliff could adjust it within seconds but I want to avoid that someone else has to work on this carb for hours because of me doing it wrong...
Mixture screws: turn equally in small increments. Counterclockwise = richer, clockwise = leaner. Wait several seconds for changes to become evident. Adjust only with engine fully warm.
How low is your low idle speed? Too low and it will roll and stall, especially in gear.
I think it's more likely that the secondary lockout or a section of the choke linkage are sticking.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
in your last pic it's the two screws at the top , that are backed by springs.(turn them in to they seat and back them out one and a halve turms to start).if you have a vacuum tester plug it onto a manifold port. set your ideal speed with the screw that is to the bottom left in you third pic also backed by a spring. start the car .check ideal speed. then check the inches of vaccum. should be in the 13 to 15 range. you sould adjust one of the two screws out a halve turn at a time to try and get the highest vacuum reading you can. also as you go, you need to keep adjusting back to the ideal speed that you want. it will increase as you screw out the mix screws. what your looking for is that highest vacuum you can get. once you fined it (mine 17 inches at 800 rpm) turn the both screws so that they are the same. (one should be at one and half, the other what ever it ended at per vacuum reading, lets say it's at three, so you have four and a half turns total, put two or so on each screw and see if the vacuum reading is the same) if not adjust both a little till you get there. that vacuum tester is a $15 item. the fewer turn out is leaner,it get better gas mileage at idlea, the more turns more vacuum for every thing. mine is at 2 3/4 turns. hope i helped.
Thanks for all your input. Jim (Fbody69) also offered some insight. I first will copy and print all your suggestions, then sit down in front of my carb and will try the easiest solutions first (I will send a prayer in case they will help...).
If it´s not the easy way, I´m afraid I then will have to drink some beers to have the nerve to go on any further... I still didn´t understand all what I´ve been told but probably I will do after a few beers...
If you ever should hear about a drunken german Firebird driver who was fished out of the Isar (that´s a river crossing Munich) where he dropped in because he couldn´t stop his car anymore -- that´s me, after several tries and errors to fix my carb. Of course, everytime accompanied by some test driving...
