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Tuning stock 340 Six Pack
#1938789
10/26/15 07:59 AM
10/26/15 07:59 AM
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Joined: Apr 2012
Posts: 364
US
f2502011
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I want to check the tune on my stock 70 340-6 automatic. Any good references out there? I have a shop manual but it doesn't have any specifics on the 340-6. Right now it runs ok but the idle seems to high to me and there is a little hesitation from light to mid throttle. I'm running 93 octane and everything is stock. I need to know what timing, idle, manifold vacuum at idle, and anything else that would help so I can get it to run as good as possible.
1970 EK2 T/A 727
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1939075
10/26/15 06:34 PM
10/26/15 06:34 PM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Posts: 36,040
Lincoln Nebraska
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there's been some comprehensive 6 pack tuning manifestos on here. see if you can retrieve em & Google it also. I'd find your stock specs for a start/baseline. Start with the AP for the hesitation & float level but I'd see what the articles have to say first. what is your idle speed? what cam?
live every 24 hour block of time like it's your last day on earth
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1939162
10/26/15 08:41 PM
10/26/15 08:41 PM
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Joined: Apr 2012
Posts: 364
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f2502011
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It's all stock. AP? Idle shows about 1250 rpm on dash tach.
Last edited by f2502011; 10/26/15 08:43 PM.
1970 EK2 T/A 727
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1939167
10/26/15 08:55 PM
10/26/15 08:55 PM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Lincoln Nebraska
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Accelerator Pump. 1250 (if the tach is accurate) is pretty high. Can you bump up your initial & lower the idle?
live every 24 hour block of time like it's your last day on earth
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Re: Tuning stock 340 Six Pack
[Re: RapidRobert]
#1939173
10/26/15 09:00 PM
10/26/15 09:00 PM
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Joined: Apr 2012
Posts: 364
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f2502011
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I'm sure I could if I knew what it was supposed to be. That's part of the info I need. The only specs I have are for a standard 340. I don't have the specs for the six pack automatic for initial timing. I need all the basic stock tune up specs, idle speed and timing for the 340 six pack automatic to establish a baseline.
1970 EK2 T/A 727
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1939270
10/26/15 10:26 PM
10/26/15 10:26 PM
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Joined: Jul 2007
Posts: 11,836
Florida
mopar346
Let me tell ya about fat chicks!
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Let me tell ya about fat chicks!
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Florida
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Factory specs were dailed back for insurance reasons and very few performance cars run best at factory specs.  I sent you a PM, I have several of the tuning docs referenced that I pulled off of Moparts, send me your e-maill address and I will ship them to you.
Careful, your character's showing!
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1939272
10/26/15 10:28 PM
10/26/15 10:28 PM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Posts: 36,040
Lincoln Nebraska
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I have virtually no exp with em & was more just providing a BTT for ya so that is as far as I can go. I hear they take time to get right but are a terror when you do get there. I just Googled "mopar 340 six pack tuning info" & it pulled up a slew of sites
live every 24 hour block of time like it's your last day on earth
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1939433
10/27/15 01:58 AM
10/27/15 01:58 AM
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Joined: Mar 2007
Posts: 3,277
West Coast, USA
jbc426
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West Coast, USA
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First get your timing correct, initial, mechanical advance, vacuum advance and limit your total timing for your tune.
Make sure you have no vacuum leaks and your linkage works perfectly.
Set your float levels, select the proper vacuum pod springs and adjust your jetting and idle A/F settings using a wideband.
It's a bit time consuming and you need to do things in order, but everything you need to know about any specific step is available right here.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Tuning stock 340 Six Pack
[Re: jbc426]
#1939552
10/27/15 11:29 AM
10/27/15 11:29 AM
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Joined: Apr 2012
Posts: 364
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f2502011
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First get your timing correct, initial, mechanical advance, vacuum advance and limit your total timing for your tune.
Make sure you have no vacuum leaks and your linkage works perfectly.
Set your float levels, select the proper vacuum pod springs and adjust your jetting and idle A/F settings using a wideband.
It's a bit time consuming and you need to do things in order, but everything you need to know about any specific step is available right here.
I need the recommended specs (for best performance) to be able to do this.
1970 EK2 T/A 727
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1939942
10/27/15 10:13 PM
10/27/15 10:13 PM
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Joined: Jul 2007
Posts: 11,836
Florida
mopar346
Let me tell ya about fat chicks!
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Let me tell ya about fat chicks!
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Florida
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With 16-20 watch your total timing, stock distributors can mechanically advance 24-26 degrees and I think the most you want to safely run is 34-36 total with the vacuum advanced unplugged.
Careful, your character's showing!
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1970717
12/16/15 09:46 AM
12/16/15 09:46 AM
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Joined: Apr 2012
Posts: 364
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f2502011
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I've finally had a chance to work on this a little more. I have 10 initial timing, idle at 950, vacuum reading is steady at 16 at idle, and the exhaust smells much cleaner. I have the outer carbs set to where there is no difference in idle if you cover the outer air bleeds. It cranks up and idles pretty well and takes fuel well if you goose it from idle. I've adjusted everything according to the references I've gotten from through here and the service manual.
I have a bog/hesitation issue when driving at low rpm/speed, easing into it until the rpms come up a bit and than it seems to pick up fine. I have the secondary rods set how the factory manual says to, but in some of the references I've read to lengthen the front rod 1
turn and shorten the rear rod 1 turn to help with hesitation. I'm not sure whether to
try this or something else. Seems just right while its idleing, but driving slow its boggy until
the rpms come up a bit. Any tips would be much appreciated.
1970 EK2 T/A 727
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1971063
12/16/15 09:12 PM
12/16/15 09:12 PM
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Joined: Aug 2003
Posts: 2,466
Answering the call of the wild
ThermoQuad
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Answering the call of the wild
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There is a guide to tuning six paks-find it-use it and you won't have to ask questions here and get piecemeal answers of sometimes questionable advice. The comprehensive guide is work of many including myself that I compiled/edited. Btw the rod offset idea you referred to is bad advice. Read the guide! Pardon my shortness -I do technical support for a very complicated product so I am very tired and I have no patience for the keyboard cowboys here who have no idea how to retain and store information from people who were kind enough to share and post it here. Copy...paste...save 
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Re: Tuning stock 340 Six Pack
[Re: ThermoQuad]
#1971325
12/17/15 07:39 AM
12/17/15 07:39 AM
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Joined: Apr 2012
Posts: 364
US
f2502011
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There is a guide to tuning six paks-find it-use it and you won't have to ask questions here and get piecemeal answers of sometimes questionable advice. The comprehensive guide is work of many including myself that I compiled/edited. Btw the rod offset idea you referred to is bad advice. Read the guide! Pardon my shortness -I do technical support for a very complicated product so I am very tired and I have no patience for the keyboard cowboys here who have no idea how to retain and store information from people who were kind enough to share and post it here. Copy...paste...save Would you be able to provide a link? Why is the rod offset idea bad advice? I've got a few different references and there is a lot of contradiction and little if any explanation as to why one approach is better or worse than another which is why I'm not sure what exactly to do. My main issue now is low rpm bog/hesitation. I haven't read anything yet except for the article from Jan 92 Chrysler Power that says to offset the rods to eliminate off idle hesitation that addresses my bog issue directly which is why that seems attractive.
1970 EK2 T/A 727
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Re: Tuning stock 340 Six Pack
[Re: f2502011]
#1972569
12/19/15 10:54 AM
12/19/15 10:54 AM
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Joined: Apr 2012
Posts: 364
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f2502011
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I've likely got a number of factors contributing to the bog and I'll need to troubleshoot each of them. One is a questionable vacuum advance which I'll replace soon. Another may be that it's running too cool. I have no idea what thermostat it has but the temp gauge barely moves up stays low and I've used an infrared thermometer and the intake stays in the 150-175 range. I also disabled the noisy heat riser and the bog seems much worse with it disabled but I'll retry it with it enabled to be sure.
As I continue to tune and mess with timing. How is the best way to modify the distributor to limit advance? Where is the slot that needs to be modified and how is the best way to do so? For each degree that I need to limit the mechanical advance so total doesn't exceed 36 do I need to shorten the slot by 0.015? To find out if my bog is from the secondaries opening too soon would it help to disconnect the linkage and vacuum lines from them and run just on the center carb to find out for sure if it's from those or maybe a faulty accelerator pump or pump setting? I need to check what springs are in the pods but if they are black and the secondaries need to come in even later to stop the bog is there a way to do that?
I'm also still curious as to why offset secondary rods is a bad idea?
1970 EK2 T/A 727
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