Thoughts and Suggestions - Idling Problem on 340 Auto W/VintageAir when Hot

[73_Cuda_4_Me]

Any suggestions on dealing with 340 Auto idle, now that I have A/C...?

Normal idle in Park/Neutral is 1100, which drops when shifted into Drive drops to 800-900...

Now when newly installed A/C compressor kicks on, RPM drops to 500-600 in Drive, engine loads up and dies slowly, or I have to throttle it to get it to go... Only does this when engine is hot, like after cruising for half hour, shutting it off for 10 minutes, then starting it up again...

It's almost like I need a step-up solenoid and cam arm to crack throttle a little more when compressor kicks on...

Anyone heard of something like this available?

[73_Cuda_4_Me]

An interesting update/thought...

I have an Edelbrock 1406 carb, and after thinking on the load-up problem, am going to try changing the 'step up' springs on the step up rods.

I am thinking that when idle drops below 800, the vacuum drops enough to allow the normal 8 inch vacuum springs to pop step up rods up enough to start feeding fuel around idle mixture screws, causing it to slowly flood out... probable cause of the 'burbling' and stall out.

I have a spring kit, and have installed the 4" vacuum springs to try out and see if clears it up...

Gonna have to take a cruise and test it, awww shucks!!!

[73_Cuda_4_Me]

Just took a 15-minute cruise, let set for 10 minutes, and started back up again...

Didn't load up and stall out with air on and tranny in drive while idling at 600 rpm... like it did earlier today...

I am cautiously optimistic that the lower vacuum step-up springs have addressed a lot of the issue!



Will keep everyone posted on results of a longer length cruise...

[Bullitt-]

I don't have A/C to compare but from an idle of 850RPM my car drops to 800RPM in gear.
Thinking that you may have a vacuum leak or perhaps the carburetor's idle transition slots are exposed.
Do your mixture screws have much effect on idle quality?

[73_Cuda_4_Me]

Thanks for this, Bullitt... I had carb off yesterday because idle mixture screw on driver's side had no effect. Took top off and cleaned... reset floats, and was able to get good idle mixture adjustments after doing that.

Vacuum check after that showed 14 when idling at 900... that is with 14 deg base timing on XE-274 cam...

I do run into the stock dizzy's mechanical advance start point over 900, so I think at 1100 idle, I am part way into it, so it compounds the drop when put into drive...

But I will check further on vac leakage possibility...!

[Bullitt-]

You might try backing off the idle screw & add a couple of more degrees of advance.
Use the vacuum gauge to find max vacuum at a lower idle & you may solve this issue.
Mal-adjustment to idle transition slots will cause one to die under load if over exposed. 

[73_Cuda_4_Me]

 

[Chryco Psycho]

Makes sense , have you checked the vacuum readings at idle in gear ?
I doubt you have much vacuum at idle & the Eddy carbs do not adjust well with low vacuum but changing the springs will help 

[Brads70]

I've used one in the past on Holley carbs .... works as it should.
https://www.holley.com/products/fuel_systems/carburetor_components/brackets_and_linkage/parts/46-74

[73_Cuda_4_Me]

Chryco - Sorry it took so long to reply, but I was at MIS for the Consumer's Energy 400, pit passes and all, thanks to my two sons! Thanks for the reply!

Just checked vacuum, engine all warmed up... with lighter step-up springs, no loading and stalling after good warmup... idles good between 650 and 800 in drive as compressor kicks on and off...

Park/Neutral, A/C Off, idle 1100, vacuum 14
Drive, A/C off, idle drops to 800, vacuum 8
Drive, A/C ON, idle drops to 650, vacuum 6

Steady cruising at 50, 2200 rpm, A/C ON, vacuum 18
Decelerate from 50 (coasting), A/C ON, vacuum 24

Brads70 - Don't know if just a solenoid would have enough 'push' on it's own to move throttle linkage at idle, would probably have to push pedal a bit to let it extend fully. That is why I was thinking a cam arm to leverage the throttle just a bit when sitting at stoplights when A/C compressor kicks in... may not need it though, from testing done so far with lighter step-up springs, but appreciate the info on the solenoid!

[Chryco Psycho]

You need lighter springs under the metering rods or it will be flooding

[73_Cuda_4_Me]

 

Thanks for the input, Chryco! It's been running a lot better since going to the lighter springs... Will be doing a long cruise tomorrow, so we'll see if I need to experiment with other lighter springs to get best part-throttle acceleration. Seems okay now, but will give it a long haul to test it out.

Appreciate all the input, fellow members!

[Chryco Psycho]

Glad to help 

[73_Cuda_4_Me]

Well, the lightest springs were too light... I had put the blue (3" vacuum) springs in, and seemed to cure the flooding, but 300 mile trip yesterday ended up with quite a bit of spark knock on light acceleration during the cruise... so indicating it was running lean on accel...

I bumped the springs up 2 steps to the orange (5" vacuum), and pinging went away, so I think things are pretty good now.

Saving up the funds to spring for EFI next!!!