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Six Pack Idle Mixture Screws Do Nothing??? #1861250
07/01/15 01:56 PM
07/01/15 01:56 PM
Joined: Jul 2011
Posts: 953
Chicago
PurpleBeeper Offline OP
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440-6 w/10.5 comp. & moderate cam & about 10-11" vacuum.

My six pack has been running pig-rich (can smell the fuel out of the exhaust) & I have been "de-tuning" the carburetors back closer to stock. The only non-stock carb parts I have now are a 3.5 power valve, the power valve holes in the metering block drilled, a Promax back carb baseplate, unplugged the front carb idle mixture screws, 3/32" holes in all the outboard throttle blades (center carb blades no holes). The power valve is brand new and I haven't had a single backfire. I'm running #64 jets & un-modified outer carb metering plates. I can get the engine to idle down to about 700-800 rpm, but my vacuum is around 5" when it's that low.

I've been trying to set the idle fuel mixture on all 3 carbs & using the "block the outer air bleed hole" method on the outboards. I started with the outboards 1/2 turn out & the center carb 1-1/2 turns out. The only real effect I got was when I closed off the rear carb (zero turns out) which made the idle go up. It "seems" moderately better with the center carb at 1 turn out both sides.

The problem is I "expected" to need the outboard carbs opened up at least a little bit and when I plug any of the outboard carburetors' outer-most air bleed holes the idle doesn't change. From what I found online that seems like the mixture is correct on the outboards.... but something doesn't seem right.... and I can still smell a little bit of richness in the exhaust and the tailpipes are a little sooty (outboards closed off & center carb 1 turn out each side).

Any ideas?


70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"
Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1861277
07/01/15 02:24 PM
07/01/15 02:24 PM
Joined: Jan 2003
Posts: 9,436
Blair County,PA
62maxwgn Offline
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Blair County,PA
One turn out on the center is not enough.Back them out about three turns,run them in until idle starts to drop off then out about one quarter turn,set idle speed then go to the end carbs.As far as smelling rich,lean will give you the same thing.

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1861602
07/01/15 10:46 PM
07/01/15 10:46 PM
Joined: Nov 2011
Posts: 238
Florida, US
72ls5fla Offline
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Florida, US
I was always under the impression if you have to low of a power valve the center carb would start to engage the metered circuit and come of the idle circuit

Maybe that's why it is running a little rich.

isnt a stock power valve something like a 6.5 ???

I'm no expert on this at all.


Got me a NEW Project
1970 GTX 440+6, 4 spd, 4.10 Dana and N96 FE5 (top/bottom) and black bucket interior.
Original transmission and Dana - Engine is a service replacement block.

Body has all stamped #s + VIN/TRIM tag and door sticker. Been hunting like all hell to find the Build Sheet.

garage find, only had 41,850 miles on ODO.
Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: 72ls5fla] #1861621
07/01/15 10:56 PM
07/01/15 10:56 PM
Joined: Jan 2003
Posts: 9,436
Blair County,PA
62maxwgn Offline
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Blair County,PA
Stock valve is 6.5,run one in my Superbird with old Direct Connection Street Hemi grind cam,vacuum at idle is around 15" hg.Get your timing right before you do anything.

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1861801
07/02/15 02:53 AM
07/02/15 02:53 AM
Joined: Jan 2003
Posts: 1,177
People's Republic of Kali
70runner Offline
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People's Republic of Kali
Very similar condition as mine; 440-6, 10.5CR, Lunati 60303, stock exhaust & iron intake manifolds, 6.5 power valve, #65jets. Idle at approx 900, 14-15" hg, 19deg initial timing, 35total. What is your initial timing? Mine starts and runs fine, but idle is rich (idling on the transition circuit), about 12 on my a/f gauge. Stalls when I try to lower the idle to get off the transition circuit or reduce initial timing. Center carb is about 2 turns out, outboards about 1 turn out. Plugging the outboard air bleeds does not effect idle (like yours).

Been struggling with this for a year or so, to the point where I'm about to try an FBO ignition system, tuned dizzy, hotter coil/spark.

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: 70runner] #1861958
07/02/15 01:05 PM
07/02/15 01:05 PM
Joined: Jan 2003
Posts: 9,436
Blair County,PA
62maxwgn Offline
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Blair County,PA
I've been doing 6 pk carbs for about 35 + yrs,any original carb that I ever got that had never had the lead plugs removed "never" had a mixture screw out more than 1/4 turn from seated.Screw adjustment is critical,1/8 turn makes a difference.Personally I would seat all screws and then open 1/4 turn and go from there,the end carbs being rich will affect adjustment on the center.

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1862257
07/02/15 07:24 PM
07/02/15 07:24 PM
Joined: Jul 2011
Posts: 953
Chicago
PurpleBeeper Offline OP
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Yes, the stock power valve is 6.5 and I've read that you should have a power valve with 1/2 your idle vacuum (mine can go as low as 7-8"). The power valve I took out was a 2.5.

My timing is set at 36-degrees total at 2600 rpm with no vacuum advance.

My outboards idle screws were completely seated when I pulled out the lead plugs. I just "expected" to have to richen them up since I drilled the 3/32" holes in all the outboard throttle blades (more air needs more fuel, right?). I drilled those holes so I could close my center carb enough to get into the idle circuit.

How can I tell if the center carb is closed enough at idle to be on the idle circuit? I'm trying to set the idle mixture(s) with the idle around 700rpm. With a 3.5 power valve I shouldn't be opening the main circuit at idle, right?

I am using both the dealer hood tach and a Stewart Warner vacuum gage I have beneath my dash, but I'm not seeing any noticeable changes turning any of the screws in or out (except when I seated the back carb completely).

Any more ideas?


70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"
Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1862682
07/03/15 10:08 AM
07/03/15 10:08 AM
Joined: Sep 2003
Posts: 348
South Lyon, Michigan
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6bblRoadrunner Offline
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South Lyon, Michigan
What is your initial timing set at (with vacuum disconnected)?

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1862795
07/03/15 01:09 PM
07/03/15 01:09 PM
Joined: May 2004
Posts: 5,123
Warrenton, VA
RoadRunnerJD Offline
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Warrenton, VA
Check for a vacuum leak

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: RoadRunnerJD] #1863050
07/03/15 08:49 PM
07/03/15 08:49 PM
Joined: Jul 2011
Posts: 953
Chicago
PurpleBeeper Offline OP
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Double-check for vacuum leak....excellent suggestion.

Timing- I just re-checked it & it was at 12-degrees advanced at idle (no vacuum) at 700-800rpm idle. I was getting a pop-pop in the exhaust on deceleration (15" vacuum) and it went away when I blocked off the vacuum advance. I just turned the mechanical advance back to about 5-degrees initial timing and I'm leaving the vacuum advance blocked off.

The exhaust is reasonably clean at 700rpm (maybe 5" vacuum) and if I turn up the idle to 1000 rpm the vacuum is 10"+ but it puffs smoke out the tailpipes that reeks of fuel, so I'm guessing ???? it has gotten into the main fuel circuit on the center carb since I uncovered the idle slot with the throttle blades open that far ?????

Anyone else have any thoughts? The vacuum leak idea makes a lot of sense. Has anyone ever blocked off the PCV vacuum port on the center carb base? I wouldn't block the PCV.


70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"
Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1863123
07/03/15 10:45 PM
07/03/15 10:45 PM
Joined: Jan 2003
Posts: 9,436
Blair County,PA
62maxwgn Offline
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Have you checked the PCV valve ?

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1863155
07/03/15 11:27 PM
07/03/15 11:27 PM
Joined: Nov 2008
Posts: 660
San Diego
formula S Offline
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San Diego
A couple things I would do is get your initial timing set to 18 deg and 36 deg total which means recurving is necessary in your case, the more initial timing you put in it the more the idle will increase allowing you to close the blades on the pri carb and getting it back on the idle transfer slots

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: formula S] #1863224
07/04/15 01:00 AM
07/04/15 01:00 AM
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Posts: 1,272
Northern Calyfornua
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Sxrxrnr Offline
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Dat's what I did, except run 20 degrees on crank. Also bought a fuel/air mixture fast tune and the little fix that replaces rear mixture screws including a clever little screw driver that allow me to access the screws. On the way, don't have it yet. Still must weld bungs to my head pipes. More accurate then running up the tailpipes.

But car runs very well and idles great at 800, but does smell a bit rich. Roller cam likely does not help In keeping the fumes down.

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1863847
07/04/15 08:33 PM
07/04/15 08:33 PM
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Posts: 953
Chicago
PurpleBeeper Offline OP
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PCV - I just checked the PCV and it's fine. I did notice that when I unplug the hose and create a massive vacuum leak the idle goes way up. Plug in the working PCV, the idle goes down. Block it with my thumb, the idle goes way down. This makes it seem like I'm still running super rich.

The floats were a little high and I adjusted them down so the fuel trickles out when running and you shake the car. This didn't seem to help much, maybe a little. Fuel pressure is 6psi.

TIMING - I actually turned the initial timing back from 12 degrees advanced to about 5 degrees. I did this because at 12 initial and the vacuum advance hooked up it was going pop-pop in the exhaust in high vacuum situations (deceleration/cruising). Now the vacuum advance is unhooked. I would like to advance the initial timing, but how do I limit my Direct Connection distributor mechanical advance?


70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"
read this [Re: PurpleBeeper] #1863936
07/04/15 10:07 PM
07/04/15 10:07 PM
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upstate western ny
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Re: read this [Re: PurpleBeeper] #1863968
07/04/15 10:45 PM
07/04/15 10:45 PM
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The Swamp
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For years I thought the end carbs only had mixture screws so that they would use some of the fuel in the bowls just to keep it from going stale, hence only being turned out 1/2 turn from the factory. And I thought my real idle quality would come from adjusting the idle circuit on the center carb. Boy was I wrong. Once I got brave enough to start opening the end carbs more than 3/4 turns I was able to jet down and turn down the mixture screws in the center carb to more 'normal' settings much like a 4 barrel. In the end my end carbs are 1 5/8 turns out and its like a brand new motor. The other hokey thing on them is getting the fast idle cam set up so it does not hang up and cause a high idle condition. I played around with the linkage and the end carb rods til I was blue in the face until I finally realized the fast idle cam was out of adjustment just a hair and just enough to make it seem like the throttle linkage was sticking open. And this is on some 20+ year old carbs that I thought were shot because I could never get it to idle decent or return to a normal idle.

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: 72ls5fla] #1863983
07/04/15 11:08 PM
07/04/15 11:08 PM
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
Mattax Offline
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Originally Posted By 72ls5fla
I was always under the impression if you have to low of a power valve the center carb would start to engage the metered circuit and come of the idle circuit

Not at all. Power valve lets more fuel into the main system. The main system provides fuel through the boosters in the venturis. Fuel moves through the boosters when the air velocity through them is high enough.

The idle systems feed off the main system, but the restrictions are in the idle system are (should be) much smaller than jets. Allowing more fuel into the main system (opening power valve) doesn't change the idle system. Idle system works off of manifold vacuum.

To the OP.
If closing the outer throttles improves idle, then consider closing off the holes. I know this is a pain, but the reason holes are used is to get the correct throttle blade relationship to the transfer slots when blades have to
be opened excessively to get good idle.

Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: Mattax] #1864401
07/05/15 05:36 PM
07/05/15 05:36 PM
Joined: Jul 2011
Posts: 953
Chicago
PurpleBeeper Offline OP
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Originally Posted By Mattax
Originally Posted By 72ls5fla
I was always under the impression if you have to low of a power valve the center carb would start to engage the metered circuit and come of the idle circuit

Not at all. Power valve lets more fuel into the main system. The main system provides fuel through the boosters in the venturis. Fuel moves through the boosters when the air velocity through them is high enough.

The idle systems feed off the main system, but the restrictions are in the idle system are (should be) much smaller than jets. Allowing more fuel into the main system (opening power valve) doesn't change the idle system. Idle system works off of manifold vacuum.

To the OP.
If closing the outer throttles improves idle, then consider closing off the holes. I know this is a pain, but the reason holes are used is to get the correct throttle blade relationship to the transfer slots when blades have to
be opened excessively to get good idle.


Actually, opening the outer throttle blades helps idle, not closing them. I had read an old trick to adjust the throttle linkage one turn loose so the outboards would be cracked a little bit open allowing you to close the center carb more. When I tried that the idle was a little erratic..sometimes 800rpm & sometimes 1200 rpm (depending if the outboards were cracked open or closed I suppose). There was no "guarantee" the outboards would stay cracked open, so I drilled the outboard holes out a little bit more (3/32" on all 4 corners) and adjusted the linkage back tight so the outboards are pulled closed.

Someone on another board suggested too high fuel level, needle/seat bad/leaking or high fuel pressure and that sort of makes sense. What should I see or not see looking down the throats of the carburetors? How would I know if a needle/seat were leaking just a little bit? I have a Holley blue and a fuel pressure gage, so I know I'm at 6psi (I've heard that's optimum) but I can turn it down to 4.5-5psi just to be sure.

THANKS EVERYONE FOR YOUR HELP!

Last edited by PurpleBeeper; 07/05/15 05:39 PM.

70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"
Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1864513
07/05/15 08:16 PM
07/05/15 08:16 PM
Joined: Jul 2011
Posts: 953
Chicago
PurpleBeeper Offline OP
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Update - Definitely no fuel flowing through the boosters in the front/rear carbs & I turned my fuel pressure down to 5psi & no noticeable change. I also set the initial timing back to 12-degrees advanced with no vacuum advance.

I was wrong before and the idle screws do "something"...sorta. On front/rear, either side, opening the idle mixture screws at all makes the idle drop off. On the center carb, turning the passenger side out 3 turns did get my vacuum back to a solid 9.5", but the driver's side idle screw still seems to do nothing anywhere from closed off to 4 turns out, so I left it at 1 turn out.

I also double checked all my float levels and they are all just at the edge of the sight hole. I've heard maybe the outboards should be a little higher, but for the moment I just want to be sure I'm not pushing fuel into the boosters from a float level too high.

How can I be positive my needle/seats are OK?

I still suspect my center carb throttle blades are open too much & maybe I should drill holes in those too??? When I turn the idle down it does seem to smell less like fuel in the exhaust, but the vacuum drops to around 7-8" (700rpm) and eventually it starts reeking of fuel again. I'm also thinking about putting in an air/oil separator in the PCV hose since I do have low-tension oil expanders and the old loose fitting TRW pistons. Blowby doesn't seem to be too bad, but I don't want to confuse any fuel puffs of smoke out of the tail pipes with oil puffs of smoke.

Keep your ideas coming....I'm so close to having a sweet running ride.


70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"
Re: Six Pack Idle Mixture Screws Do Nothing??? [Re: PurpleBeeper] #1864569
07/05/15 09:12 PM
07/05/15 09:12 PM
Joined: Jan 2003
Posts: 9,436
Blair County,PA
62maxwgn Offline
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62maxwgn  Offline
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Posts: 9,436
Blair County,PA
if opening the end carb screws makes the idle drop off,it is too rich.How far did you open the power valve channel restrictions in the metering block and what metering plates are in the end carbs ?

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