A/C idle question

[RCCDrew]

So my Cuda has A/C. I have it idled up to 1400 rpm with no load. When I pull it into gear with the A/C and fans on it wants to die. Did the factory address this with a stepper motor? How do people with retrofit A/C systems deal with this?

[Chryco Psycho]

the fatory used a solinoid to increase idle speed , but having yours at 1400 sound wrong by 1400 you are probably running off the jet circuit not he the idle circuit , so with the rpm drop you are off the jet circuit & the idle circuit is not working properly , so you need to address the idle vacuum / power valve seletion & maybe drill  holes in the throttle plates so get thhe engine running properly on the idle circuit then it will handle the A/C load much better & should idle around 800 rpm

[1 Wild R/T]

So my Cuda has A/C. I have it idled up to 1400 rpm with no load. When I pull it into gear with the A/C and fans on it wants to die. Did the factory address this with a stepper motor? How do people with retrofit A/C systems deal with this?

Stepper motor.... In 1970 the only engines using a stepper motor were on the Saturn V..... 

http://hubgarage.s3.amazonaws.com/photos/5271819/EDELBROCK_AC_SOLENOID_CORRECT_SPRING_01_-6_20_2012_detail.JPG

[RCCDrew]

Stepper motor.... In 1970 the only engines using a stepper motor were on the Saturn V..... 

http://hubgarage.s3.amazonaws.com/photos/5271819/EDELBROCK_AC_SOLENOID_CORRECT_SPRING_01_-6_20_2012_detail.JPG

Thanks for not helping at all.  . So how did my dads 69 383 Fury with AC idle right with the AC on as opposed to off?

[734406pk]

If you have an Edelbrock/Carter/Weber type carburetor, you can use this Idle Speed Control solenoid:
http://www.summitracing.com/parts/edl-8059?seid=srese1&gclid=Cj0KEQjw6Ya5BRDdyOewyo_Z_64BEiQA-fVKe1OVRIdGGmn5cONs52XRvGpRYeiJO1tsNk-sX-2HX4saAv578P8HAQ

But as pointed out by CP, if your idle speed is 1400 rpm and stalling when the A/C clutch engages, something is wrong and needs to be addressed first. What model engine do you have and how is it built (stock, mild or wild etc?).

[YellowThumper]

X2 on above comments.
There should not be enough load to stall it out like that. How is the engine build? Do you know what your idle vacuum is?

[RCCDrew]

Mild 340, .484 purple shaft, stock converter, edelbrock 750. You may be right. I'll reset the idle and see what's up.

[734406pk]

Mild 340, .484 purple shaft, stock converter, edelbrock 750. You may be right. I'll reset the idle and see what's up.

That's a substantial cam for a 340 cid. Have you owned this car for long or is it fairly new to you? My first thought is you may have a vacuum leak somewhere. Does this car have factory power brakes?

[RCCDrew]

Yes, has power brakes. I didn't build it, but have had it for a while. And when I say dies, it doesn't die right off. I mean it idles at about 400 rpm for about 15 seconds then will eventually die. But when it's hot it idles about 1400 rpm with no load. Idles good with AC off.

[734406pk]

Yes, has power brakes.

You may want to check if there is any leaks in the power brake booster. The easiest way is to remove the vacuum line from the power brake booster check valve and plug it completely. Start the engine and check your idle speed, see if it has changed (lower rpm). If you have the test equipment, you can vacuum test the power brake booster for leaks. This is a very common vacuum leak source on these 40+ year old cars.

[Chryco Psycho]

You need to get the idle around 800 rpm first , at 1400 you are running on the main circuit not the idle circuit  , this is the root of the problems you are having   , the 484 cam is long duration & will not make much vacuum.
 Having a 750 Eddy carb is the worst choice , these carbs are horrible to make work with low engine vacuum ,  so what is happening is the metering rods are jumping up & flooding the engine so you want the lightest springs available under there for starters . raising the floats from 7/16 to 3/8 will help too . restricting the brass tube on the idle circuit is a must too but very difficult to do , you can solder the tubes closed & redrill much smaller if you have tiny drill bits , I still think you will need to drill the throttle plates as well to get more air flow with the throttle plates closed enough to make the idle circuit work  .

[RCCDrew]

Both good points. I will check out the booster tomorrow.
The carb and cam weren't my first choice, but what I got the car with. Any recommendations for a cam? I want to swap to FI TBI probably after the Power Tour. Also will swap to the late model (302?) head from the J heads in time. Just trying to get a little more driveability for the time being. I'll also start on the carb. I have a carb spring kit but I forgot what's actually in the carb. I will check that out too when I have time.

[734406pk]

It sure sounds like you have a bad mix there! Your not alone though, if that makes you feel any better. Since you are going to EFI eventually, i would recommend checking your brake booster for vacuum leaks now so you don't inherit that issue with the EFI swap in the future. Just my 2cents.

[Chryco Psycho]

Well the Lunati VooDoo series will get you more lift with less duration which is a win win  702 or 703 sounds about right , with EFI often you have to run open loop @ idle to run a preset program until you hit 1500 or so & go closed loop to make things work using a map sensor .
 The later heads are 308 for 360 , the smaller 318 heads are 302

[73_Cuda_4_Me]

Where is your initial timing set at for idle??? Are you running stock distributor setup??

You might be experiencing similar problem I had with my 74 340 w/mild cam... if you try to set timing at close to factory 'normal', cam won't like it, and falls off under load... advance it enough (like 16-18 deg advance) for best vacuum at 800 rpm in Neutral (tranny pumping). You should only get about 200 RPM drop when A/C kicks on, according to my manual... (I don't have A/C on my 73).

At 1400 RPM, you are already on mechanical advance curve on stock dizzy... so any drop in RPM pulls timing back, which compounds the RPM drop with that cam!

Check timing shift at idle for load/no load variation... you might have to add stiffer advance springs to move advance curve higher in RPM range so you aren't fighting yourself with that cam...

Just IMO...