Because you have created a large vacuum leak, it will work fine if you just pull the PVC valve out of the cover.
Richard
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| Car won't idle during valve adjustment https://www.slantsix.org/forum/viewtopic.php?t=41783 |
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| Author: | 74DartSport [ Mon Sep 06, 2010 4:14 pm ] |
| Post subject: | Car won't idle during valve adjustment |
Yesterday afternoon my son decided he wanted to adjust the valves on the 74 Dart. I had him read how to do it on this forum, and off we went. I sent him to find a golf tee to block off the distributor vacuum tube, and he removed the valve cover, took the pie pan off the carburator, and we began. After showing him how to hold the wrench and the feeler gauge while the rockers are going up and down, we cranked the car several times and it kept dying if you allowed the car to idle. We spent the entire time revving the engine up to keep it from dying while one of us adjusted the valves. Really made the adjustment more difficult. The valves were actually very close to specified .010 intake and .020 exhaust. Once the car was buttoned back up, we started it and it idled fine without having to rev it up. I wanted to know why the engine kept killing during the valve adjustment, so while idling I pulled the distributor vacuum tube hose at the distributor. No effect on the engine. I put it back and then pulled the closed crankcase vent tube at the base of the Holley 1920. The engine died. Put it back and started the car, and it idled fine. Why does the engine die when the hose to the PCV valve (crankcase vent tube) is not connected to the carb? One last thing. The golf tee I had my son get. He never plugged the distributor vacuum tube during the valve adjustment. Will this affect the valve adjustment? |
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| Author: | Fopar [ Mon Sep 06, 2010 6:01 pm ] |
| Post subject: | |
Because you have created a large vacuum leak, it will work fine if you just pull the PVC valve out of the cover. Richard |
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| Author: | ceej [ Mon Sep 06, 2010 6:53 pm ] |
| Post subject: | |
The valve adjustment won't be affected by having the idle running a bit wild. It just makes it more of a knuckle buster. Pull the pcv from the valve cover to avoid the vacuum leak. If it won't come out easily, get a new grommet for it, or plug the PCV hose fitting at the base of the carb. Your idle may drop a little, which will make things easier.  CJ |
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| Author: | 74DartSport [ Mon Sep 06, 2010 9:51 pm ] |
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Quote: The valve adjustment won't be affected by having the idle running a bit wild. It just makes it more of a knuckle buster.
Maybe I didn't explain clearly. The pcv is new. When I did the valve job, the valve cover was off and the other end of the hose disconnected at the base of the carb. This is when the engine would not idle without dying unless I kept it revved up. I completed the valve adjustment without any problems. Once the valve cover was reinstalled, and the pcv hose reconnected to the carb, the car idled fine. After reinstallation, if I pulled that hose off the carb base, the car would die.Pull the pcv from the valve cover to avoid the vacuum leak. If it won't come out easily, get a new grommet for it, or plug the PCV hose fitting at the base of the carb. Your idle may drop a little, which will make things easier. CJ I do not know why the car required higher revving to keep it running during the valve adjustment. Are you saying the car had a vacuum leak because the valve cover was off and the pcv valve was disconnected during the valve job was the reason the car required higher revving to keep it idling? Sorry if this is a dumb question. I just want to know. |
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| Author: | Fopar [ Mon Sep 06, 2010 10:13 pm ] |
| Post subject: | |
Yes, with the hose off the carb it is a big vacuum hole. |
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| Author: | wjajr [ Tue Sep 07, 2010 5:06 am ] |
| Post subject: | |
74 DartSport, A vacuum leak becomes less problematic as the throttle plates are opened to wider angles. The volume of air increases through the carburetor, and makes the vacuum leak become less disruptive of the ideal fuel-air mixture. In other words; at idle, that free flowing air from the PVC port becomes substantial in comparison to the amount of fuel & air delivered by the idle circuit. Once the engine gains rpm and throttle opening, the leak looks smaller & smaller in comparison as more fuel & air flows from the main metering circuit & through the carburetor; because that leak flows a constant volume of air. Next time just plug off the PVC vacuum tap with tape, or rubber cap, and the engine will idle down nicely. You won’t have to plug off the vacuum advance tap because it only pulls vacuum once the throttle plates have cracked open a little bit & the engine is turning somewhere above1000 rpm. |
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| Author: | 74DartSport [ Tue Sep 07, 2010 1:57 pm ] |
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Understood. Thanks for everybody's assistance. This forum still has very useful helpers. |
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