Slant-6 idle problems, need advise.....

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Doug Palmer

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My Dart's 225ci w/single barrel Holley-1920, has a problem idling when the A/C is on and the car is in gear, stop lights, etc... The carb was rebuilt last month and seems to works well when driving the car or when it is in "Park" and it is idling. The slant-6 has an electronic ignition. Any help would greatly be approciated.... Doug :read2:
 
Could be vacuum leak, idle not set high enough, or timing. Could also be the compressor getting ready to lock up...
What is the idle - in N or park with A/C on vs A/C off.
Welcome aboard Doug :cheers:
 
I am not sure how they did it with the older cars but the new computer controlled ones raise the idle when the a/c is turned on.

On the older ones maybe this is accomplished with vacuum, not sure.
 
I know the 1920 on my 73 didn't have an idle kick solenoid like modern cars do. I want to say I've seen some late 70's carbs with kick solenoids on them.
 
I would look for a vacuum leak. More than likely you will find one at the intake gasket nine times out of ten. Take some brake cleaner and spray along the gasket at the head. If the idle jumps up when sprayed you found your problem. Good luck!
 
Thanks guys, I will be trying all your suggestions in hopes of fixing this thing..... Doug
 
My '69 Dart 225 w/ Holley 1920 never idled right until about the 4th carb I put on it. This was thru several head jobs, an intake manifold swap, and even a new long block. It was the carb all along. You can find other horror stories about badly rebuilt carbs on www.slantsix.org. It always idled lean, which causes stumbling and missing. Rich usually runs smooth until it dies or pours black smoke out the exhaust. One way to tell is that it idled best w/ the max spark advance I could give it, >30 deg, though the factory spec'ed more like 10 deg advance. I checked that my damper marks were correct w/ a dial indicator on the piston, thru the sparkplug hole. Good luck.

The other thing that drove me nuts was the choke pull-off diaphragm at the top of the carb. Once older and smarter, I learned that the choke plate should be closed when cold. Once the engine fires, the choke pull-off gets vacuum and pops the choke plate open slightly (to drill size shown in the manual). The problem is the diagphram rubber fails, especially when hit with carb cleaner. Check w/ a vacuum pump. You can buy just the pull-off. Carbs are quirky beasts.
 
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