1973 440 Stalls out when hot with A/C on

The_Eagles’_Nest

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So after driving my Imperial for a couple weeks or so a concern has developed. The car will run great in the morning and runs great when going down the road, and in stop and go traffic without the A/C on.

However as soon as I turn on the A/C it starts to run much more roughly and it will actually stall after coming to a stop with prolonged A/C use.

I have replaced the fuel filter, air filter, PCV valve, and changed oil as part of maintenance.

I double checked timing and set it at 15°BTC, idle was set at 700 rpm in neutral with the A/C on and high beams on, with the vacuum advance disconnect.

I went to go investigate this as I suspected a fuel issue or a vacuum leak. After confirming great fuel delivery, I decided to look at the ThermoQuad. Looking inside the carburetor then bowls had minimal sediment, almost negligible. Then, I found the choke shaft has radial play and the primary throttle blade shaft has radial play.

I would like to see if anyone else has had similar issues. I’m 99% sure that a new carburetor without wear will resolve this issue.
 
Does the A/C have vaccuum controls? Could it have a leak in a valve, hose or diaphragm? Just a thought. I wiuld want to eliminate the "simple stuff" before throwing parts at it. Lindsay
 
Does the A/C have vaccuum controls? Could it have a leak in a valve, hose or diaphragm? Just a thought. I wiuld want to eliminate the "simple stuff" before throwing parts at it. Lindsay
It is auto temp. I have checked for vacuum leaks. No leaks.
 
If you don't find an immediate reason, maybe add a idle kick up solenoid. I have a client asking if I can do that for his car.
 
I’m pretty sure that the primary throttle shaft having any play, let alone almost an 1/8” in any radial direction qualifies as an obvious reason.

It makes sense to me since the car will lean out as it gets hotter and a vacuum leak from the throttle shaft will make it worse.
 
All throttle shafts have "clearance" between the shaft and the carb base plate. We were told, years ago, at a Holley carb seminar, that such movement is figured into the fuel calibration for the carburetor. Therefore, do not worry about it. Kind of like the calibrated vacuum leak a pcv valve causes.

IF the throttle shaft is very loose, there might be a carb shop which can bush the primary throtle shaft so you can retain your current carb on the car. To me, that would be the best option as any reman/replacement TQ I've seen is pretty much "one size fits all". So getting a reman TQ might cause more trouble than you currently have.

If the throttle shaft was worn and moving around very much, I would suspect the throttle plate relationship to the idle and transition ports would be off, causing MORE drivability issues than you now have. Is there a "hot idle compensator" on the carb and is it working correctly? Is it a bi-metal spring or a solenoid run by a temp switch?

One other option would be to "clean up the underhood area" of the TQ and related items. Replacing it with a TQ-clone (in more ways than one) Street Demon 650 carb on the existing intake manifold. With the "phenolic bowl option" and electric choke, of course! You would then have to adapt the new carb to the linkages and check the air/fuel ratios (might need the related "Strip Kit" from Holley).

Might the a/c compressor being putting more load on the engine than normal?

Just some thoughts,
CBODY67
 
I understand that throttle shafts have clearance, this one has enough play to affect the transfer slots. I realize that any competent carb shop can check and rebush the throttle body. However Carlisle is in two weeks. No carb shop has that turn around time.

I have a remanufactured 4160 on my 72 and it is the best running carburetor I have ever had. No issues out of the box, it fired up and idled perfectly. It needed the floats fine tuned but that was it. I don’t understand the disdain for remanufactured carburetors when many people don’t even give them a chance.

I do not know if the A/C compressor is good or bad as far as load goes. No one locally has the means or sources for parts to rebuild an RV2 compressor and I just bought my own R12 machine because the only guy who had one just got rid of his and said he just vents R12 to the atmosphere. Classic Auto Air wants $800 for a rebuild and I can’t pull that money out of my butt. I cannot compare it to the 72 because the air never worked on it.
 
My dislike of reman TQs is not that they might do a sub-standard job in rebuilding them, or use flaky parts, it's just that when you look up one, it is a "one size deal", rather than one for 360s, one for 400s, or one for 440s, plus all of the varieties of OEM emissions hardware and such which each one should have. The TQ has many things which are better than the "rival" QuadraJet from GM. Although GM carbs usually have bulletproof drivability, in spite of the small float bowl on the QJs. Plus their tendency for the power piston to get gummed-up from very easy "high vacuum" driving. Some of the earlier model years got fantastic fuel economy, but other ones did poorly, by observation.

There might be a TQ reman vendor whose carbs are more-tailored to the engine and model year, but I suspect most will be in the "will work" orientati0on than not.

Have an enjoyable and safe trip to Carlisle,
CBODY67
 
If you don't find an immediate reason, maybe add a idle kick up solenoid. I have a client asking if I can do that for his car.

I agree. If not equipped with an idle step up solenoid install one. When the AC is turned on the solenoid increases the idle speed to compensate for the added load of the AC. If it is equipped with one is it working and or is it set up correctly.
 
I agree. If not equipped with an idle step up solenoid install one. When the AC is turned on the solenoid increases the idle speed to compensate for the added load of the AC. If it is equipped with one is it working and or is it set up correctly.
It does not have one. It has no evidence that one was ever installed and it looks like the original carburetor. It is a 6322 which is a 440 carburetor. Dated 364 2 which coincides with the Jan 18th build date.
 
The Imperials did not have one from new, But should not be a hard install. I will check my manuals to see when it was introduced, a 74 Challenger with AC had it.
 
I understand that throttle shafts have clearance, this one has enough play to affect the transfer slots. I realize that any competent carb shop can check and rebush the throttle body. However Carlisle is in two weeks. No carb shop has that turn around time.

I have a remanufactured 4160 on my 72 and it is the best running carburetor I have ever had. No issues out of the box, it fired up and idled perfectly. It needed the floats fine tuned but that was it. I don’t understand the disdain for remanufactured carburetors when many people don’t even give them a chance.

I do not know if the A/C compressor is good or bad as far as load goes. No one locally has the means or sources for parts to rebuild an RV2 compressor and I just bought my own R12 machine because the only guy who had one just got rid of his and said he just vents R12 to the atmosphere. Classic Auto Air wants $800 for a rebuild and I can’t pull that money out of my butt. I cannot compare it to the 72 because the air never worked on it.
If you buy a reman thermoquad from summit, go through it checking specs and part numbers.
I also spray my gaskets with fluid film so I can take apart easy if I have to.
On your leaky carb, maybe if you try some grease around the shafts to see if that changes your vacuum leak. Just temporary, but will confirm or deny your diagnoses.
My 73 440 is at 20 initial with a 35 total and I still only get 15" of vacuum in gear.
 
If you buy a reman thermoquad from summit, go through it checking specs and part numbers.
I also spray my gaskets with fluid film so I can take apart easy if I have to.
On your leaky carb, maybe if you try some grease around the shafts to see if that changes your vacuum leak. Just temporary, but will confirm or deny your diagnoses.
My 73 440 is at 20 initial with a 35 total and I still only get 15" of vacuum in gear.
Mine was on 2° or 3° and at 600 in neutral. I bumped it up to 15° and set it to 700 in neutral and it was idling smooth.
 
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