6 pak slow return idle/poor throttle response

[tak419]

Title should have said No Crisp throttle response.
Let me start by saying I've Google and searched the heck out of this, tuned on this forever and can't find the issue so any help is GREATLY appreciated.
440 basic stock rebuild and carbs bought around 1998 new. Car starts good, and runs decent. 4-speed car.
Timing at 10* initial/37* Total. Mopar Electronic dist also bought 1998.
12lb vacuum. Fairly steady.
850-900 RPM idle. Idle set with outboard carbs disconnected.
Outboard 1/4 turn out
Center 1 3/4 out. Set to highest vacuum

Here's the issue, the throttle isn't crisp and it returns to idle slowly, not super slow but not fast. When driving and floored it does have power and can feel the outboards kick in so that's working. No back fires, but does have a slight, I mean slight stumble when revved up fast for an idle only.
I've read the sixpack tuning guide and a lot of articles, done a lot of research. I don't have a problem tuning a carb and rebuilt the engine myself, actually very mechanical.
I'm asking the sixpack experts if they think this is vacuum leak related or something out of adjustment cause I can't find the issue after 5 yrs of screwing with it.
Also, I have checked for vacuum leaks. What am I missing ??

 

[BSB67]

Title should have said No Crisp throttle response.
Let me start by saying I've Google and searched the heck out of this, tuned on this forever and can't find the issue so any help is GREATLY appreciated.
440 basic stock rebuild and carbs bought around 1998 new. Car starts good, and runs decent. 4-speed car.
Timing at 10* initial/37* Total. Mopar Electronic dist also bought 1998.
12lb vacuum. Fairly steady.
850-900 RPM idle. Idle set with outboard carbs disconnected.
Outboard 1/4 turn out
Center 1 3/4 out. Set to highest vacuum

Here's the issue, the throttle isn't crisp and it returns to idle slowly, not super slow but not fast. When driving and floored it does have power and can feel the outboards kick in so that's working. No back fires, but does have a slight, I mean slight stumble when revved up fast for an idle only.
I've read the sixpack tuning guide and a lot of articles, done a lot of research. I don't have a problem tuning a carb and rebuilt the engine myself, actually very mechanical.
I'm asking the sixpack experts if they think this is vacuum leak related or something out of adjustment cause I can't find the issue after 5 yrs of screwing with it.
Also, I have checked for vacuum leaks. What am I missing ??

Still sounds like a vacuum leak. Have you removed the intake?

 

[tak419]

Yes had it off once. I've sprayed everything from water to starting fluid checking for leaks. I'll definitely check again.
That's been my thought is a vacuum leak because of it coming down to idle slow, but I've always had it in my head that a vacuum leak will result in a crap idle. Have I been wrong in that ?

 

[bigbluedodge]

You said basically stock. Is it a stock cam? Will it idle lower than 850?

 

[tak419]

Yes it will idle lower.
I don't remember the exact cam but it came from the mopar parts book 20 yrs ago. It was one lift higher than what the stock cam for the sixpak was listed at. I know it was smaller than the 509 because I was worried about vacuum. So basically stock cam.

 

[BSB67]

Yes had it off once. I've sprayed everything from water to starting fluid checking for leaks. I'll definitely check again.
That's been my thought is a vacuum leak because of it coming down to idle slow, but I've always had it in my head that a vacuum leak will result in a crap idle. Have I been wrong in that ?

If it is a vacuum leak:
When the intake is off, close inspection will show if and where it is leaking. If it was leaking before, and you installed it basically the same way, it is likely still leaking. IMO, spraying stuff is a very poor way for finding difficult vacuum leaks. Hand over the carb is much better IMO, and has never failed me.

If it is not a vacuum leak:

• Add more initial timing.
• Open the outboard carb idle mixtures to 1/2 to 5/8 open (irrespective of what the "tuning bible" says)
• Make sure you have enough mechanical advance timing spring tension to make sure that the advance weights are not wondering around at idle rpm.
• Adding vacuum advance might help.

Without knowing the cam with certainty, you'll never know how much, if any of your challenges are simply cam related.

At some point, consider just putting a different induction system on for awhile to get past your frustration and enjoy the car, then come back to it when you're ready.

 

[tak419]

Hand over carb ? I'm not dumb to the idea but exactly how on a six pak will that work ? Do you try and cover just one at a time or a couple ? I've heard of using block off gaskets on the outers for tuning but never read into it that far.
After I try the hand over carb thing, (give me the procedure BSB67) I can try bumping the initial timing up, I can bump the idle up and check when the mechanical is really kicking in. I'm pretty sure it's way past idle but at this point I'm willing to try everything.

 

[tak419]

Anyone willing to throw a phone number out for a call to help out.

 

[BSB67]

Yes it will idle lower.
I don't remember the exact cam but it came from the mopar parts book 20 yrs ago. It was one lift higher than what the stock cam for the sixpak was listed at. I know it was smaller than the 509 because I was worried about vacuum. So basically stock cam.

For many "one step up" in MP cams would be the 280° - 0.471" cam. This is a bit more than a small step up IMO. Much larger duration and tighter lobe separation angle. It should be perfectly fine in your 4 spd car, but it will have noticeably more idle attitude than a stock cam. And that is assuming this is the cam that is in it. There is also the 284° - 0.484" MP cam which is larger, but still smaller than the 509.

 

[tak419]

The .484 sounds familiar but it's been so long ago I don't remember.

 

[bigbluedodge]

My first excursion into performance cams was a .484 lift purple shaft. My car was an 440 automatic with a stock converter and a single Holley750 when I started. I think the fix for poor low end response (hesitation) was advancing the initial timing. If I remember correctly, I wound up with 16 or 18 degrees initial and modifying the vacuum and centrifugal advance until I wound up with 34 degrees total.

I might have disabled the vacuum advance, though (it was 25 years ago).

 

[mac]

is it the mallory guts in the distributor with the small weights and light springs? i eventually got rid of that and purchased a reman distributor for a 1972 440. that got me the larger weights and heavier springs to hold the advance steady at idle. anyway i would definitely increase the initial to around 18 and total at where you have it now, 37. after that reset your outboard carbs as suggested to 1/2 turn. the reset middle carb idle mixture. see how that sounds. that's my 2 cents.

 

[Officer Higgins]

http://sixpacksixbbl.homestead.com/mrsixpack45.jpg

 

[tak419]

is it the mallory guts in the distributor with the small weights and light springs? i eventually got rid of that and purchased a reman distributor for a 1972 440. that got me the larger weights and heavier springs to hold the advance steady at idle. anyway i would definitely increase the initial to around 18 and total at where you have it now, 37. after that reset your outboard carbs as suggested to 1/2 turn. the reset middle carb idle mixture. see how that sounds. that's my 2 cents.

Did Mallory make the Mopar electronic distributor at one time ? Tomorrow I'll pull it apart and look. Are the springs color coded ?

 

[mac]

i forget the time period that those internals were used in the electronic conversion kits. i tried using the keys used to adjust the total timing and i found a set of springs that came with a chart to guide you in the proper choice for your application. i struggled to get a consistent setting using this distributor. check to see if this is that type of distributor. here is a link to setting up that type of distributor.

http://board.moparts.org/ubbthreads/ubbthreads.php/topics/1055401/1.html

i just want you to be able to get the initial timing set without over timing it so you can get some road tests in.

 

[mac]

here is the kit i was talking about. just double check that this is your situation.

https://www.summitracing.com/parts/dcc-5153446

 

[AR67GTX]

For the slow return to idle does the car have the stock dashpot on it - a canister/spring affair on a bracket that has a plunger that hit the center carb throttle linkage? It would be on the driver side and sit below the car close to the intake. I think they were stock on some or all six pack intakes. But that was their purpose - to slow the return to idle. If it's too aggressive it can be adjusted - even to the point of disabling it.

 

[mac]

For the slow return to idle does the car have the stock dashpot on it - a canister/spring affair on a bracket that has a plunger that hit the center carb throttle linkage? It would be on the driver side and sit below the car close to the intake. I think they were stock on some or all six pack intakes. But that was their purpose - to slow the return to idle. If it's too aggressive it can be adjusted - even to the point of disabling it.

i think you are referring to the idle solenoid that deactivates on shut down to completely close throttle plates to help with stopping dieseling. used mostly for stock appearing setups. as far as i know it does not ease the throttle back to idle. it is used instead of the idle speed screw.

 

[tak419]

Hi Mac. You're correct it doesn't have anything to do with the throttle crispness or returning slowly back to idle .yes mine has it and that isn't an issue. I'm getting ready to get the distributor apart and check what's inside. I'm not sating this isn't the problem but I think my issue is more towards a vacuum leak I can't find or something out of adjustment with the carbs. But as before I'm gonna check everything mentioned by you all because I sick of not having a snapping running engine. It runs great, starts good, definitely plenty of power and outers open up nice at speed. It's just this slow idle return that is annoying.

 

[Paul_G]

Lots of ways to check for a vacuum leak. Let me add another. A simple propane torch. Turn it on, unlit of course, have some gas flowing out, pass it around the gaskets, seals, and mating surfaces while idling and listen for changes in idle rpm. Let some gas flow in the center carb just for kicks, you will hear the idle raise. It is a dry method, and wont hurt anything. If there is a leak, as the propane gets sucked in the engine rpm will rise. It has worked for me many times over finding difficult to find vacuum leaks.