idle problems, please help restore my faith in quadrajets!

[casual dreamer]

I changed the idle tubes to help my idle problems, and now my idle screws do nothing at all, I can bottom them out and the engine still runs, first it was the right side, now its both sides. Is it possible I put something on wrong? What could cause my idle circuit to not work now? I am about ready to give up on this carb, it has been nothing but problems   what should I do? I really want to like this carb, please help! Thanks!

[429bbf]

please include some information . carb no. vehicle, what all you have done to carb etc.and some one will try and help you. fwiw

[Ethan1]

I changed the idle tubes to help my idle problems, and now my idle screws do nothing at all, I can bottom them out and the engine still runs, first it was the right side, now its both sides. Is it possible I put something on wrong? What could cause my idle circuit to not work now? I am about ready to give up on this carb, it has been nothing but problems   what should I do? I really want to like this carb, please help! Thanks!

 What is your setup and specs of the car?

[casual dreamer]

The car is a 68 Chevy caprice 327 275 HP TH400 trans all original. The carb #7029223 IY 1409. My friend rebuilt it about 2 years ago, it has always had idle problems, I always blamed the idle tubes since they were not changed. I changed them the other day, now I can almost seat the mixture screws completely, it idled terrible and the only way it will run is with the throttle open. It will not idle with the throttle turned down and the exhaust smells bad. I wonder if I put something back on wrong. Any advise would be great, I am very frustrated with this carb and I really need to get this car going again (its my daily driver) thanks!

[Bigal442]

I'm not an expert but thought I would throw out some ideas. Based on the exhaust smelling bad and the rough idle it sounds like you are running rich at idle. You might pull out a spark plug or two to see if they are black and fouled. You might also consider pulling off a vacuum hose while the car is running to see if the idle improves. Just don't pull the one that goes to your distributor. Pulling a vacuum hose off will introduce more air to the system. If you're running rich then adding air should make it run better. Also make sure the car is fully warmed up and not running with the choke involved.

If your running rich the first thought would be to turn the mixture screws in to cut fuel. However, if your engine is not running fully off the idle circuit you might be pulling fuel in through the primary circuits instead. When you lean out the mixture screws by turning them in you could make it even worse by forcing more fuel in through the primaries. I recently experienced this. I would look down on the primary throttle plates while the car is running and see if you notice fuel dripping on to the top of the throttle plates. A flashlight will be needed for this. This is known as "nozzle drip". I believe this is evidence that your system is pulling fuel in from the primary circuit because the throttle plates are engaged too much because of the idle stop is turned in too far.

I would start with adjusting your mixture screws at about 3 or 4 turns out and set the engine speed to about 700 rpms by turning the idle speed screw. Next check to see if you have the nozzle drip. If you do, see if you can add more fuel through the idle circuit by turning the mixture screws counter-clockwise. Then try lowering throttle plates by backing off the idle speed screw while keeping the rpm's about the same. Again check for nozzle drip.

The main objective is making sure your engine is not pulling fuel in from the primary circuits at low idle. If you can't get it to idle just through the idle circuit your likely not getting enough fuel through the idle tubes, the channel restrictors or through the mixture screw holes. Something may be clogging the path that is used for idle fuel.

Al

[429bbf]

give this a try . pull both idle screws out and blow a little compressed air in the holes . don't get carried away. also what size were the tubes you took out ?what size did you put in?fwiw

[Cliff Ruggles]

Did you install the same size idle tubes as the ones removed?

Is the gasket sealing well between the main body and airhorn.  Any leak there can and will effect idle fuel delivery.

Vacuum leak someplace?  Another contributor to poor idle problems.....Cliff