Hi All,
Here's a problem that we can't figure out. Car is the 72 Comet, 250 (4.1) six. It runs OK at speed and does not miss once it is moving. Lately the idle quality has gone WAY down. We just can't keep it running. Very intermittent. The carb idle adjustment seems to make no difference, like there is a massive vacuum leak. It just acts like a couple of cylinders are cutting out intermittently. Here is what we have found and done.
1. Rebuilt the carb and even replaced it with another one, fresh rebuild off Ebay. The replacement carb has more of a flat spot on acceleration but idle quality is the same. We put in a new carb base gasket. New fuel filter. Gas is good, not stale.
2. We had a Duraspark II distributor on it, with the blue grommet. The idle timing was moving about a bit so I took it off. The spark plugs all looked about the same- no evidence of fouling, gapped at .040-.045, maybe a bit lean.
3. We put the old points distributor on it, set the dwell and timing. New wires, new plugs. Timing at idle (high idle- maybe 1500) is 10-15 degrees. It speeds up when you move the timing but still has that miss. The vacuum and centrifugal advance both work well. No leaks in the diaphragm of the advance unit.
4. There is a log type fitting under the carb, connected to the intake manifold. The hose going to the vacuum controls for the heater/AC doors was cracked so I just plugged the fitting. Line to the vacuum modulator for the C4 trans was good, no leaks. The shifting is good also, so that isn’t the problem.
5. The PCV valve was replaced, no change. If you take the valve out of the valve cover the poppet is bouncing back and forth like it is supposed to so the PCV system is not at fault.
6. Tried to find a vacuum leak with both WD-40 and propane gas methods. It didn’t make any difference.
7. We are using the original ignition coil. It is the only thing we haven’t changed. I would think if that were the problem it wouldn’t run well at high speeds. I may jumper from the battery to the hot side of the coil to bypass the ballast resistor and ensure full voltage to the coil.
Please help, this is Mikey’s first car and he really likes having something different to drive, especially one he works on for himself. This car used to run good, but something has changed. I’m losing confidence on this vehicle. I’ve been working on Fords for over 40 years and this one has me stumped.
Karguyz
Here's a problem that we can't figure out. Car is the 72 Comet, 250 (4.1) six. It runs OK at speed and does not miss once it is moving. Lately the idle quality has gone WAY down. We just can't keep it running. Very intermittent. The carb idle adjustment seems to make no difference, like there is a massive vacuum leak. It just acts like a couple of cylinders are cutting out intermittently. Here is what we have found and done.
1. Rebuilt the carb and even replaced it with another one, fresh rebuild off Ebay. The replacement carb has more of a flat spot on acceleration but idle quality is the same. We put in a new carb base gasket. New fuel filter. Gas is good, not stale.
2. We had a Duraspark II distributor on it, with the blue grommet. The idle timing was moving about a bit so I took it off. The spark plugs all looked about the same- no evidence of fouling, gapped at .040-.045, maybe a bit lean.
3. We put the old points distributor on it, set the dwell and timing. New wires, new plugs. Timing at idle (high idle- maybe 1500) is 10-15 degrees. It speeds up when you move the timing but still has that miss. The vacuum and centrifugal advance both work well. No leaks in the diaphragm of the advance unit.
4. There is a log type fitting under the carb, connected to the intake manifold. The hose going to the vacuum controls for the heater/AC doors was cracked so I just plugged the fitting. Line to the vacuum modulator for the C4 trans was good, no leaks. The shifting is good also, so that isn’t the problem.
5. The PCV valve was replaced, no change. If you take the valve out of the valve cover the poppet is bouncing back and forth like it is supposed to so the PCV system is not at fault.
6. Tried to find a vacuum leak with both WD-40 and propane gas methods. It didn’t make any difference.
7. We are using the original ignition coil. It is the only thing we haven’t changed. I would think if that were the problem it wouldn’t run well at high speeds. I may jumper from the battery to the hot side of the coil to bypass the ballast resistor and ensure full voltage to the coil.
Please help, this is Mikey’s first car and he really likes having something different to drive, especially one he works on for himself. This car used to run good, but something has changed. I’m losing confidence on this vehicle. I’ve been working on Fords for over 40 years and this one has me stumped.
Karguyz
Great news. Thanks for the update.
