Six Pack outboard vacuum

I cant leave well enuff alone so I put a fun gage
On my outboards to see what color opens where
plotting vs rpm .
Any one ever observe vacuum signal and
opening rate , or you too busy holding on ?

The 6bbls I’ve run on the dyno always used the pretty soft springs, and the secondaries would pop open surprisingly early when opening the throttle while bringing the motor up against the load.

Never bothered to take a reading off the secondary vacuum lines though.

Isn't the vacuum line from the center carb to the out board carb vacuum pods, just to give a small kick to start the opening?

Digger73 (Mike)

Neither can I nor can i find data ..
either way at 2.5 they start to tip in
And then once when i was really into it , theres was no reading , but boy they opened.
Wish i was a Holley engineer , lol .
After 20 + years of six paks, im gettin there ...

Just playin with springs and makin notes ..
i got this feeling when I put stickier tires on , Ill be doin it ALL over .

I put a small bolt or screw with a nut to lock it down in the return slot about half way full open on the center carb to start them opening when I hit throttle to WOT
Me like this lot, this is a old NHRA stocker trick

I ran purples on my old 440-6. 588 solid roller cam, 3800 stall. zero hesitation.

That sends venturi vacuum to the vacuum pods. Then both end carbs have what they call a bleed hole which helps pull stronger venturi vacuum from the end carbs after they start to open to stenthen the venturi vacuum signal even more. Some people plug the bleed holes in the end carbs so the ends carbs will start to open sooner but it wont get the extra vacuum once they start to open. The bleeds in the end carbs are basically like a vacuum bleed off until the end carbs start to open and then they help to pull stronger vacuum as the signal will then be from all three carbs. Ron

I guess I have a pesky old set
I guess that come with 50+ year old carbs .
Outboards open up great in 2nd-4th gear
under load .
Lighter springs didnt change quickness to open .
Just cant seem to get them to open up on a
1st gear burnout..
Maybe not enough load . ?
But the first to 2nd gear shift opens them.
I dont need to roast the tires off the rims , but
surprised I cannot in first gear.
Dont get me wrong . Its hazes tires for 100’
But not John Force style .

As far as cruising and normal accelerating
It is just about as fast as my Hellcat . (Not joking )
Wondering what im missing in the final tune ..

Go pro camera made me prove im running on center at most times .
Thats the coolest thing ive ever watched and streamed
to my smart tv...

if you have '69 carbs then they will open slower than the '70-'71's. pretty sure '69's have a larger kill bleed and a smaller orifice in the center carb that the vacuum hose hooks too. carb list #"s with a -1 after them was supposed to take care of that issue.

I got my very first 6bbl because of the very issues being discussed here. A guy had bought a 4 year old 70 440-6 Cuda. Nice car, but was just old enough that the secondaries were inconsistent on their openings. Sometimes yes, sometimes no. None of us knew much of anything about that stuff back then. He messed with it, had others mess with it and soon enough, it was all messed up.

He became so frustrated with it that he offered to trade for the 340-4 in my 70 Cuda. My 340 was nothing special, only had a set of hedders, but it did run good. I really liked his set-up although I didn't know much about it. So we swapped everything in our cars, from the radiators to the trannies.

After a bunch of reading and experimenting, I did get the carbs to be more consistent. Added, cam, hedders, etc. Man, that thing was a monster. Street raced it for years. I even spun rod bearings and drove it home knocking. Pulled the pan and offending rod cap, polished the bearing off the crank and put it back together....in the car. Did that 2 or 3 different times.

But, like others have touched on, it had to have some traction (load on the engine) to get the secondaries to open.

This. And any vacuum leaks anywhere in the "system" that actuate the carbs will affect their opening too.

All vacuum tite
Unless its internal in 50 yo carbs ...
i guess i wanted to be cool and run numbers carbs
when i have fresh ones on the shelf

I like abusing myself i guess , lol
Thanks for the toughts .

Its still scary fast, but just not john force fast on the
line..

Did you check for vacuum leaks. If so, how did you do it?

Fair question .

Ive used propane listening for a rise in idle , and even watched
the tach from timing lite .
Ive yet to do that with a hot hot engine .

Ive Sprayed bottle water to see if it was drawing in.

Other than that , are there better methods . ?

I paid a lot of attention to the outboard pod
Connection to bodies .

Just because , ive done the suck test on the outboards tee hose.
They do open in unison with kill bleeds plugged or not .
This is irrelevant kind of , because i know they open.

I think ive been thorough or im missing a better
More accurate method .

there's nothing wrong with '69 carbs for performance. just understanding there is a difference may answer some questions. the '69's with the slower opening also used a purple spring which is one step heavier than the '70-'71 yellow spring. just swapping to the yellow spring will cover at least half the difference and the truth is the difference between the two is no "make it or break it" deal.

So Andy... The problem is that they won't open in first gear some of the time? But the always open in second gear?

You haven't over tightened the baseplates? When you manually open the center carb after the engine is hot (engine off) do the secondary's "crack open" or are they completely free and smooth?

Those things you did/checked have no bearing on the outboard carbs opening. A leak in any part of the outboard carb vacuum system would go completely undetected with what you did.

Do you have the 69 carbs as Lew asked?

Not only do they have the larger kill-bleed like Lew mentioned, the outboard throttle plates can stick in the throttle bores as mentioned, particularly in the 69 carbs. Also as mentioned, over torquing the base plate can cause binding. You can simply check these by hand with the engine off.

I've always done the 600 grit paper thing to the end carb throttle blades no matter what year they are. in fact I think the new carbs are worse than the old carbs for binding.

Yes they are 69 1/2 carbs
Hoses
Nipples
Connections to main body
Seal between carb and pod have been gone through
Note, and this particular set of carbs have been
Gone through by maxwgn


Please elaborate on a more specific independent
vacuum test on the outboard components and your suggestion .

I was assuming you thought a poor base seal or
Other would/might cause this issue .. thus the propane test .

If there is a method , lmk .

HI Tom , How are you ?
Yes weird deal , I suppose .
This ONLY happens in 1st gear at a start.

Baseplates dont seem to be warped on a flat table , I usually use a hand nut driver to titen the carb bolts .

I manually drew open the carbs so I can observe my outdboards opening and snapping shut .

I just confirmed , both outboards crack open a " c" hair when i open up the center . Engine is cold .

I readjusted my rods lengthened / shortened to double check their placement , still same result outboard crack open.

with engine running ,they DO NOT open .

Heres the weird thing that leads to Possibly a vacuum leak somewhere .

I have a gage hooked to outboard tees . cruising and tipping in slightly on acceleration on any gear other than 1st , I read 2.5-5"" of vacuum and
you can feel the the outboards opening .

I might need to learn how to vacuum test the carb itself.

The first gear issue happens with Polyglas OR wide fat sticky tires . So The engines definitely under load on a burnout.

Im not sure if this is because of a short 1st gear ( passon OD )
Im chipped at 6500 , maybe i should go 7 ..

ill test the secondarys after a run around the block and see results .

the secondaries should not open/crack open or anything with movement of the center carb throttle shaft. this will really screw up idle/low rpm run. look for a burr or something were the carb linkage screw rides in the throttle arm slot. jimmy jack Studebaker may have put a screw in there at sometime to get the carbs to open sooner and boogered the slot. those connecting rods should never be tight but have a little up and down movement at closed throttle.

Engine UP to 195

opened center

Front outboard stays closed , rear outboard opens just a hair ( promax baseplate ) I wonder if any relation..

no movement whastosever on outboards with engine running ..
only with Engine OFF

What rear gear? Being that it's a 4 speed, I'd imagine even with 3.55s it would be pretty short and lots of tire spin. I'm guessing it's load related

My 6 pack blows through first so quickly I doubt the vacuum is held long enough to open the secondaries before I shift to 2nd.

If you suck on the pod vacuum hose then close the hose off with your tongue while holding the kill bleed closed with your finger the throttle blade should stay open. If it does and doesn’t bleed down you don’t have a leak.

As a quick test, place a strip of duct tape into the throttle bore and cover the kill bleed hole on both front and rear carbs.

Take it for a ride.

no movement with the engine running is correct.

Maybeee spot on , thats why im wonderin if i should adjust the rev limiter to 7k
But not sure — 354’s now

Itll do wheelies with 4:10’s .. lol

Some interesting reading here

The rest of the story

This

Andy, I can tell that I never liked the Promax Baseplates. While the throttle bores are the correct size it's the blades that aren't shaped correctly. I'll say those bases came and went in popularity. Everybody I know that bought one currently has it on a shelf. The problem with them was... In a drag race you couldn't rely on your carbs to open.


If it were me I would swap the Promax base out with a stock one and I would also measure the size of the kill bleeds. Take off the vacuum pods and shove a wire gauge or get out your 60 to 80 drills and make sure Dr. Drillbigger hasn't been in there working his art. If they are jacked up you just fill them with JB Weld and drill them to the proper size. I would love to find the article that must have been written back in the day instructing six pack owners to drill that passage. Like to see who wrote it... And strangle them


My money is on the baseplate though.

Yep
Nothing like chasing your tail . Youre right

The promax baseplates were a good idea

But these i had milled for me work much better ..

I always Seem to revert back to factory stock engineering

and its most consistent .

, it was an elephant in the room.

seems that folks who get 6paks think that gadgetizing them is the cure for not understanding them or how to tune. I think the most important thing to keep in mind with a 6pak is they are not a race induction system. they are at their best as the premier street and strip induction system. if one needs maximum race performance then use a race intake/carb combo. this isn't to say you can't use a 6pak in a pure race combo but just keep it's limitations in perspective and don't try to make it what it's not.

And these were very discrete and cool
..

Thanks for all the replies
Never hurts to post data to refresh
memory from cars sitting all winter .

Back to factory baseplate

lol .. next post , stay tuned .. how do I get the duct tape out from between the planes of intake ..

I think it would be cool to try. Ive never done that . , it sounds like I can for a day temporarily be John Force after a duct tape mod. .

This all helps to more understand how it all works in unison ..

Tom , or others .. do you swap / have different kill bleed carbs for polyglas racing vs regular fat tire racing ? or rely on springs only ..

The tape trick is temporary. If it works then you know you don’t have a leak but a “combination” issue.

Combination of spring rate, kill bleed size, vacuum, etc.

There are guys running SS 6BBL cars going deep in the 9’s, no apparent issues with the carbs.

I realize the tape is temp .

Glad that you stated that the carbs are used on 9 second cars .
Ive seen and read in other places . But unfortunately
not commonly seen , everyone swears by 4 barrels .
I prefer to do it the hard way .

I guess ill know im good if I can run 10’s on slicks and cruise
On the street reliably .. have to be faster than hellcats .
Tough with a stick ..

The particular quirks with particular carbs are new to me , but tuning the carbs not.
The big cams always complicate it for most .
And an aftermarket or mechanical glitch will drive u nuts .

In response to getting the tape out between the planes of the manifold - make that piece of tape long enough to cover the kill bleed then come up over the air horn of the carb and past the air cleaner gasket flange. The air cleaner lid will hold the tape from being sucked in the engine.

My car in Stock Elimator back in the late 70’s ran 11.50’s in NHRA trim.

9” tire, auto, factory lift hydraulic cam, blueprinted short block and heads using STOCK internals, factory pan, factory intake - race weight was 3725 lbs. on the starting line. I can’t drive it on the street without any problems today.

Using all the stuff available now, cams, more ratio, ported heads with bigger valves, etc. you should have no problem running tens.

Piece of cake.