al714

hello

I have a problem with my quadrajet. Car was acting great, then i noticed that the rpm were lowering as days passed by.I know its not a timing issue just got a new timing chain and everything was set right and still is .Engine is stock (1972 cutlass supreme 350). Well when i tried adjusting the mixture screws the one by the driver side as i turned it the rpm moved, but the one by the passanger side as i turn it nothing happens.Any suggestions? Should i just get another carburetor(thinking about buying one from national carburetors) previous owner said he rebuit it.. but dont know if he did it right.

Rickman48

You probably have a vacuum leak - check all the hoses to the carb, and if one slips off very easy, and you've some length, cut it square with a pair of sidecutters, and push it back on.
If that doesn't help, get a can of carb cleaner and spray it around the carb while running - if idle changes, look there for your leak.
Make sure all screws and bolfs are tight, too.
Good luck!

MDchanic

Consider that there may be a piece of crud stuck in an idle passage on the passenger side - it worked its way into place, slowly blocking the flow, and now there is very little fuel coming out that idle port, so adjusting the screw doesn't help.

It would be reasonable, after checking the vacuum connections as Rickman says, to take the carb apart, blow through everything, and recheck all the adjustments. If it was recently rebuilt, you can probably get away without any new gaskets.

- Eric

Rickman48

You might also try the old "manual choke" trick.
Rev and hold the engine, after warm-up, at about 3-4000 RPM.
MANUALLY put your left hand over the carb, until it almost dies, and remove your hand before it does. Take it back to the same RPM, and do it again, maybe 3-4 times.
Have had that straighten out a few carbs over the years.

al714

I sprayed carb cleaner around the carb and no rpm change. Also around the brake booster cause I heard sometimes they leak from there.I did noticed that when I put my hand over the carb the rpm went up.didn't completely cover it up.. Think it's what md said that there might be debris inside

Rickman48

If it idled up, it's not getting fuel to the unadjustable side - hence clogged passage!
Try the 'manual choke' thing - it may just suck it out!!
Won't hurt anything!!

al714

I tried what Rick suggested. But no change except that in park the cars rpm are starting to change. But not as much

al714

Another thing I noticed is that in the morning when I drive the car it acts normal.. Any ideas?

W70442

Would spraying carb cleaner directly into the carb possibly dissolve or dislodge the crud, if there is some crud there?

al714

Ok I took the carb out the car and took the carb apart and cleaned it out.. Installed it and carb still wont change when adjustment screws are moved..is there something else that can effect the rpm.. Or maybe I just need a new carb

W70442

As you pointed out, when you put your hand over the carb, the idle went up. When the engine is cool and when it is cool outside, like in the morning, the choke is activated which causes that flap on the top front side of the carb to close doing the same thing as putting you hand over the carb.
The screws on the front of the carb are ONLY for the idle circuits. While you will notice a slight change in the idle adjusting them to their extremes, they do NOT set the idle speed. That is done by adjusting the screw under the throttle lever on the driver side.

The fact that the rpms raise when you cover the carb(engine is warmed up and choke is off, right?) does indicate that the carb is running lean.
You could still have something clogging the pass side idle circuit but it is pretty common for those adjusting screw threads to get stripped. You may be turning the screw but it may not actually be going in or out. Try monitoring the screw closely when you turn it to make sure it's actually moving in and out.

brown7373

What do you mean when you say "you cleaned it out"? When apart, you need to spray a carb cleaner through each and every passage in the carb, meaning each and every pin hole sized hole. You should have cleaner shooting out the opposite end. Also blow compressed air through the various passages. And do it in both directions on each passage.

It sure sounds like an idle passage is blocked and needs cleaned out. Until that is fixed, your idle mixture won't properly adjust. As Rickman48 suggested, upping the rpms and holding your hand over the carb might disloadge the blockage, assuming it can be drawn through the idle circuit. But maybe it needs to be blown the opposite direction, which can only be done with the carb apart.

MDchanic

AND, you need to take out the mixture screws before you do it.

- Eric