250/AT Car started running rough to the point it wasn't drivable. A full tuneup, as it was needed regardless - plugs, wires, cap, rotor, set points, carb rebuild and car was still running rough. Checked compression - all good. I realized I forgot PCV. Pulled original PCV and car ran smooth. Installed new PCV and the car is back to stumbling bad. No vacuum leaks. What am I missing?
If it runs OK with PCV blocked, likely the valve is passing excessive amount of air. Newer ones are hit & miss at best, I've used 2.3L 4cyl Mustang valves on V8.
If I pull the hose off the valve, the car levels out and runs smooth. So smooth you can lay your hand on the roof and not feel the car is running. Plug the hose back onto the valve and it starts coughing and running bad.
Removing hose from PCV valve creates a HUGE vacuum leak(or at least supposed to), results in poor running. If engine smooths out with leak, likely have a serious carb problem. Does it really smooth out or seem so because engine speed increased?
While the PCV is connected, the engine runs rough at idle and through al RPMs. When the PCV is removed from the line, the car smoothes out completely, of course the idle speed is slightly higher. I was leaning toward a failed rebuild or a worn out carb, but was looking for confirmation before moving forward. The car has been driven about 300 miles since the carb was rebuilt. Performance has just declined since.
So as a follow up. 74 250. All stock. Full tune up, new pcv, reman. carb installed. The car ran good, but did have a very small miss. Drove it around, put about 15 miles on it. Put a tank of gas in it and the car began stuttering like previously. I assumed bad gas, drained the tank - inside is spotless, I think this tank was replaced in the last 10 years, blew out the fuel lines, new filter and changed out the carb. The car is still running bad, at idle and under acceleration. Running extremely rich - blue smoke out the tail pipe. I've checked compression previously, all was good. Replaced all ignition components. Where to go from here? Did I get a bad replacement condensor? Something else I overlooked?
Have you verified that the choke is working properly and not staying closed? If so, you might need a new carb...
You never said anything about replacing the condenser. You “ set the points”. Check dwell? Timing? I think your headed in the right direction about fuel system. I would think if you replaced the carb with a reman and the engine started to run better, I would think your issue is in the delivery, rusted fuel Lines creating a problem with dirt in the carb. Have you removed the top of the carb and visually checked what or if anything was in the bottom of the fuel bowl? You don’t have to remove the carb completely to do this.( I never had to and I’ve been around since these were still on the road!)
so if the vacuum hose is left completely disconnected (I am assuming you don’t plug it when you take it off the PCV) the car runs great? Sounds like an idle mixture problem. Check your throttle blade opening and idle mixture screws, I like to screw the screws all the way in and count the rotations and then open them back up to your original setting and go from there. If you do plug the PCV hose when you disconnect it and it runs better then you have a faulty PCV that is stuck open and causing a super lean condition. Did you reset your timing or remove the distributor at all? Sometimes a loose distributor will turn a little and be way out of time.
