6 Pack Carb Idles well with Air Fuel Idle Screws Closed

Looking for some guidance here. I have a recently rebuilt 440 with a slightly improved cam and msd ignition with billet distributor. Exhaust is stock manifolds with TTi exhaust pipes.

The carburetors are the aftermarket version of the correct 6 pack carbs. They were recently rebuilt and tested on the bench. All in all the carbs work well with no stumble under hard acceleration but the carbs were running rich at idle.

The car starts well either cold or hot but always runs rich. I closed the idle air/fuel mixture screws on both sides of the center carb and expected the car to stumble so I could start to adjust but no stumble occured and most of the rich gas smell went away. I also had to lower the curb idle screw so that the idle was at 900 while in drive with foot on the brake.

A friend tells me that I am not running on the idle circuit and the carb must be giving the engine gas in some other way.

Why is the carb running and idling well with the air fuel idle mix screws entirely closed? This seems strange but in reality the car seems to run well.

Also, any opinions on whether center fuel bowl breather tube should be connected by a hose to the valve cover breather or left unconnected and no hose.

thanks for all the help.

Power valve is either ruptured, wrong PV gasket, and or wrong valve and gasket, there are 2 different PV/gaskets asseblies for the Holley

Run it to the valve cover if you wish?, using a 2 or 3 nipple breather, as far as leaving it open, an engine/carb fire is possible, not good...so I would put a vacuum cap on the fitting, won't effect anything

Mike

Thanks Mike. I will take a look at that.

Funny. I had a cap on it and someone told me that was wrong and must be left open or vented to breather cap on valve cover. Sounds like I will put the cap back on since my breather has only one port and that goes to my six pack air cleaner port. Thanks again. I think mancini's tilde me I could cap that port when I bought the single port breather.

Great advice.

100% with Dayclona. and until you fix the power valve issue you're pretty much chasing your tail. been there done that exactly with a leaky and wrong power valve.

You need to check your idle vacumn to determine which power valve you need, manifold vacumn holds the valve closed, not enough allows the valve to open and enrich the mixture. Usually a good rule of thumb is to check your idle vac and if it is, say 10", you would use a power valve marked 5 or 5.5. Since the carbs were rebuilt, I would also check the idle mixture screws on the end carbs, they could be open too much and be contributing to the overich idle. About 1/2 turn out from seated is a good start.

I have several sixpack cars all have the breather/vent on the center's bowl plugged with a vacuum cap, no issues, left open is what the factory did if the carb was vented and there where no provisions or requirements for evaporation control....left open you have a greater chance of a carb fire, and with the faster evporative rate of today gasoline, it's just drying up faster in the bowl if sitting for some time, which leaves you with crusty contaminates to foul the carb's passages...something you don't need esp on a multi carbed vehicle

Mike

Capping of the enclosed bowl vent valve hose fitting defeats the purpose external bowl vent valve.
The purpose of the vent valve is to provide an external path for the fuel bowl evaporation to improve hot starting. Without the idle bowl vent valve, all fuel vapors collect in the air cleaner through the main bowl vents, creates an over-rich hot start condition. Problem with six-packs, two other fuel bowls without external venting, still a beast to start hot with the air cleaner in place.

Agreed, but I'd rather deal with a hot start condition (never experienced that on a sixpack set up, don't jinx me...lol!) than the possibility the needle seat sticks and fuel leaks out the uncapped vent, sprays or puddles on the engine/manifold and the possibility of fire

Mike

As far as hot start,33 + years,no matter what temp,turn key,couple of rev's and drive it away !

can you up the initial so you can lower the idle speed? 900 just seems high for a mild cam. how many turns in is the idle speed screw? I would cover the basics, float levels/float saturation/float linkage hanging up/fuel psi at idle/power valve blown. all that is left is the idle circuit(s). 6pack newbie but iirc all (3) are contributing to the idle mixture provided to the eng & it's all gonna add up (1 eng but triple the carbs "amount" of idle fuel)

Robert,nothing wrong with the 900 idle speed,it is actually the factory recommended specs for 6 pk with idle solenoid engaged,evidently he has other issues.

Likely, not enough initial timing, factory specs are not good unless you have to smog test it. Throw the book numbers in the trash and tune it properly, it will run a bunch better.

They tend to like 16-20 initial using a stock camshaft. Cleans thing up a bunch! Tailor mechanical advance to hit your total number and run it.

He's at 900rpm in DRIVE!!!

OP, read this. There's some good info.

http://www.moparts.org/Tech/Archive/fuel/7.html

Not wanting to get into the middle of this "expertise / knowledge" contest but, HMMM???


https://board.moparts.org/ubbthreads/ubbt...umb.html#UNREAD

I was reading down this thread thinking someone must be gonna come up with this. I agree, first thing to check and adjust. Engine possibly not running on idle circuit causing idle mixture screws irrelevant.

Since you have to disassemble to replace the power valve it would be best if you base-lined your set up by using the guide to tuning six paks. A member here [sogtx] is the six pak guide testing dept. He just set up [base-lined] a set of carbs for an unknown 440 six pak. To the amazement of the shop experts where the car is living it started up,idled & ran beautiful the first time. Nice work Andy!

I don't think the bowl vent is the problem here, but as always you cannot troubleshoot a set up with out it being base-lined. Everyone who tries to help forgets this and tries to jump in in the middle of the problem. This is not criticism just an observation. I wish one of them would link every six pak inquiry to the guide so I would have more time to ride [mcycle]. As I work in Technical Support with very complicated technology we achieve proper results with the least amount of pain by starting at the beginning. Thanks to the Lift Off Hood Playground for posting the guide.

how to make the six pak work

Noted!

i think the issue is there are many variations or updates floating around on this site.

I did click on the link & had a copy sent to me. No plans for one but someone might ask me to look at there's. If I did run one I'd have the air cleaners poking thru the hood just for the cool factor.

Thanks for all the excellent knowledge. I will go through each and every response to try and understand what is happening and get back to guys.

This may sound stupid but can an incorrect fuel pump contribute to this issue. Say, too much fuel pressure damage the PV or affect the outboards too? I guess I just had too ask.

What is the preferred fuel pump and fuel pump pressure among the guys on this thread?

Thanks again.

Black there are no dump Q's. yes too high of pump psi wont bother the PV but it will overpower the needle/seat assys & cause a rich idle. eddys dont like more than ~5.5 lbs. Holley can handle higher

holley are good up to about 7.5. are you running an electric or mech pump now?

Mechanical.

It's a carter not quite sure model number but will get it. It's not the 6 pack pump that I see many recommending, the carter 6 pack pump with two cylinders. The pump on the car has one cylinder with two ports. I started the car today and car is still smelly but fires up well and seems to drive well. Still haven't pulled off the carbs but will be working through all the issues that everyone has identified.

Doesn't surprise me that carbs could be way out of adjustment.. Just because someone rebuilds them and bench tests them does t mean they know what they are doing. They never asked me about my vacuum at idle or what cam I was using so I do have a lumpy cam which may have lowered my vacuum below factory specs. I also have a 1500-1800 stall sped on my converter so I will get those specs too. All I know is that I got put my foot into it to make it go from a dead stop.

I am at 900 rpm in park and 700 in drive. As I recall I had set initial timing to 18 degrees btdc and since I am using msd I do not have vacuum advance on the car.

Looking forward to figuring this out. Thanks again for al l the help and support.

More initial MAY help. my stock '83 318 had 18. post how things turn out

Where are idle mixture screws on end carbs set to. They could be supplying too much fuel at idle causing center carb setting to be irrelevant. They should only be barely screwed out from full in. Mopar carbs of course had them leaded up so as not to be messed with unless you really knew what you were doing.

What is idle vacuum, are you certain of no vacuum leaks. Could be several competing issues, not only just 1. Choke completely open?

OP, what list number carbs are you using? Also are the lead plugs in the base plates on the outboard carbs. in place or removed? If removed reset the idle mixture screws to 1/3 to 1/2 turn out from bottom. Adjust them in sofly, DO NOT OVER TIGHTEN THEM IN If there not removed remove them now and adjust them in and see how that helps I've owned and ran a bunch of different OEM sixpaks on both BB and SB Mopar, they will idle on the outboard carbs only Welcome to the woderful world of Six Paks AKA, you will need to get the outboards carbs idle mixture set up adjusted properly before using the center carb. for the final tuning and idle speeds Make sure and remove and reset the carb. linkage on the drivers side to insure the outboards are closed all the way at idle with the the choke opened all the way, block it open if you need to The key to success on these working good is in ALL the details

Gentlemen

It's been a while since I posted but I just wanted to follow up on this situation. I haven't driven the car much since the first posting and subsequent replies but wanted to let all know where I am today on this. First, thanks for the help.

The car idle like a pig with low vacuum, somewhere around 10-12 hg. The engine bounces around like it wants to jump out of the car until it warms up. Still a really bad fuel
Smell.

So i grew a pair and took the carbs off to check settings and power valve and jets etc. I went through the the guidance by Tom quad from the a12 lift Off Registry website.

When the carbs were redone before Putting them on the motor, the carb guy said they were setup and ready to go. Well, he doesn't know what he is doing!

Outboard carbs were each set 3 turns out so I backed them down to 1/8 CCw. The center carb had #68 jets so I put in #64 just so I could baseline. I checked the power valve and it
Seemed there was fuel in the space behind it so that made me think it may be bad. I replaced it with a 4.5 which is lower than 6.5 but remember my vacuum hg was low so
I wanted to be sure. I can always go back and put a higher Pv in. I did
Not check of verify float levels yet. Also my fuel pump is the Carter street fuel pump Which the a12 site recommends.

Well, results? After snugging everything up nice and firm and starting the engine......I had a dramatic improvement, which I was hoping for.

The engine woke up and started right away with a very smooth idle and a steady vacuum of about 20 hg. Also I forgot to mention I set the center carb idle mixture to 1.5 ccw. The idle rpm was 1500 but i expect it to be higher which I can adjust that down with a further
Timing and vacuum tuning.

I couldn't check the fuel float levels since the idle was so poor so that's my next job and then I will further tune to get max vacuum at an idle of around 900-1100 Rpm in gear.

Voila, I know have control over the idle circuit on the center.carb. and no more fuel smell. I will also be replacing the spark plugs and the engine oill before I Try to further tune
For timing, vacuum and idle. I'm sure the plugs are Fouled beyond belief.

The lesson of this story......pull the carbs and verify everything to the 6 pack carb checklist and don't take anything that your carb rebuilder tells you as accurate. The only way to figure these things Out Is To Understand them and learn from these threads where people that have these carbs can share info.

I do believe the power valve was faulty but I will check it it on a mighty Vac gauge.

The moral of this story..... a rich condition at idle and no control over main carb idle
Circuit, check out board carbs to ensure 1/8 ccw and check that pv is working, 6.5 is appropriate for most engines with Hg of 12 or greater. Also, make sure everything is
Nice and snug but don't gorilla tighten. I turn everything till it stops under normal exertion. If I have to grit my teeth or out my body weight on it, then I'm Over tightening.

If overich condition persists after correct carb set up then verify fuel pressure is
Not Too much and float levels are adjusted correctly. For my situation, an accurate carb setup remedied my rich condition so I'm assuming my fuel pressure is fine and floats just need verification. I do have a slight bog under firm acceleration but I believe that's my 4.5 pv and I will be going back to a new 6.5 pv once I have everything dialed in for good.

By the way. As i was removing the carbs I noticed some less than tight fasteners so
I imagine i had some Vacuum leaks too

Now, I have an entirely different car that doesn't disperse crowds like a tear gas canister. It idles well and I have control over the idle circuit..

Thanks All.

A happy ending! its too bad that shoddy work by some gives the rest of us a bad rep.

It is good that you took the time to learn what was really causing your problems
Now go out and drive it before changing the plugs, they should clean up real well unless they are fouled bad enough that they miss all the time Drive it like a non hot rodder for the first ten to fifteen minutes to allow the gunk to burn off the plugs and then, in a safe place, get after that rascal with full throttle
Let us know how it drives now

that guide is awesome for setting your base line. great piece of work!

Thanks

Thanks

Thanks

I still have a ways to figure this site out. I thought I was thanking each of you individually. Guess not.

I will update my progress as I continue to dial in the carbs. I know I have more work to do but know i can at least work on it safely and have guide to refer to. I realize I'm only halfway down this road but the car runs so much better. Lookin forward to figuring this out entirely and getting the most out of it. When these 440s run well, there's nothing like it!

Thank god the older kids I hung out with before I could drive in the 70's and 80's were into mopars!

Stay tuned.

Where in this wonderful state of Illinois are you?

Chicagoland.

That's cool 3XBlack! Keep having fun with it and you will be one of the experts on these things!

Thanks for vote Of confidence