jaunty75

When I first got this car running again a couple of months ago (403 engine), it didn't really have this problem. When cold, I would push the gas pedal to the floor and release, and the car would start right up and idle fast and smoothly as you would expect. As it warmed, it would slow down, and everything was fine. I could drive the car without a problem.

But lately, the engine won't stay running after it first starts. When cold, it will still start and idle fast just fine and just as before, just like a cold engine should. But if I tap the gas pedal to kick down the idle speed, or just let is slow down on its own as the engine warms up (but I'm usually out driving it by this point), it will start to stumble and have difficulty staying running. If I put the car in gear, the idle will drop low enough that it will almost certainly stall. I can restart it, but I have to keep my foot on the gas to keep it running.

One other clue: when it starts to stumble, traces of black smoke come out the exhaust, so I'm thinking the engine is flooding. Stuck choke? Waterlogged carburetor float?

I have not tried anything yet to fix this. I thought I'd throw this out there and see what suggestions people might have. This car does have about 10 miles of vacuum hose, and I've not replaced any of it yet. It's all old, and some of it is certainly stiff and in need of replacement. I've got hose ordered in the four different sizes I measured and will get to replacing it as it comes in. I'm certain that vacuum leaks could contribute to or cause idling problems. I'm also going to disassemble the choke to make sure it's clean and operating properly.

My thought on why this problem was not evident when the engine was first started after a decade of not running but has become a problem later is that running the engine has heated everything up for the first time in years, and the rubber isn't so pliable any more. As the engine heats and cools, the rubber is not expanding and contracting as it should.

Just thoughts.

Thanks.

damaged442

Old fuel? Water in it? Ethanol? Crap from tank plugging stuff up?


I think your vacuum lines could be an issue too though, just trying to see what else could be a potential issue.

Olds64

You could always spray ether around the carburetor and vacuum lines with the car on high idle to see if you have a vacuum leak.

tru-blue 442

Could be as simple as a plugged carb filter or pcv valve. Or a crack in the vacuum
line from it under the carb. It is a meticulous service to perform, but I would suggest replacing all the vacuum lines being careful of the ones that have plastic male ends on them. I use an exacto knife to split them, not twisting and pulling.

jaunty75

Thanks for the suggestions. I don't think it's a fuel delivery problem because the engine runs at high idle but not at low. I would think that if there was a fuel delivery problem, the opposite would happen. I once had a loss of power at highway speeds with my '67 Delta 88, and that turned out to be due to a dirty fuel filter. I had recently worked on the fuel system (dropped and cleaned tank, replaced sending unit and fuel pump), and any time you do that, you stir up crud that can get sucked through the lines, so a fuel filter change is a good idea after driving a few miles after doing that kind of work.

I did replace the fuel tank, sending unit, rubber fuel lines, fuel pump, and fuel filter on this car, so I think fuel delivery should be good. I just changed the fuel filter again a couple of days ago for the heck of it. It's $3 and five minutes of work.

But I DO think it is a legacy of old fuel and a long (10 year) sit. I think I have either a choke problem or a float that's either stuck or has a hole in it, causing a flooding problem. As I said earlier, the continued running of the engine has awakened sleeping dogs and stirred up some long-dormant crud in the carburetor.

I was looking at youtube videos about carb rebuilds, and one showed a guy rebuilding a Quadrajet on a '79 Malibu that had exhibited the same symptoms my car is. He removed the carb, and the bottom of the float bowl was covered in crud from old gas. It was causing the float to occasionally stick, among other problems, and the engine to flood.

I have decided to man-up and rebuild the carburetor. After viewing those videos, I think I can handle it. I did rebuild the carb on my '67 without any problems. That's a 2-barrel and this is a 4, but it's the same kind of job. The rebuild kit and a new float are ordered. I've also ordered about 40 miles of vacuum line in about 10 different inside diameters, so I should be able to blanket the car in new vacuum hoses.

I also found an excellent youtube video that not only explains which ports on a quadrajet are ported vacuum and which are manifold, but also exactly what each port is typically hooked up to (PCV, EGR, vapor canister, brake booster, etc.). This will be very helpful because some of the lines on this car are either not connected or not connected where they should be, I don't think.

Olds64

You should be able to rebuild the Q-jet without any troubles. Once you rebuild the carb and replace all of the vacuum lines I bet it runs like a champ. Keep us posted.