How much carb is too much carb

[Viewsonic]

Hello all. So like the title says, how much carb is too much carb? It got me wondering if i have too big of a carb or i got something else going on.

I have a 69 sport satellite wagon. I pulled a 383/727 out of a 68 fury. It has a freshened upper end, but stock bottom end. I have an edlebrock torker intake and a rebuilt holley 4 barrel, single pumper carb. (3310-3 series, electric choke, vacuum secondary). I have gone through and verified that the points are set correctly (gapped and cleaned) and that the timing is set to 10 degrees (as per factory, for now). I have 12-13 inches of vacuum, i have size 74 jets in the carb with a 6.5 power valve, dont recall the squirters size, but i think they are a 38? I am running right close to 13.7 /13.9 air fuel ratio (as with a AF meter on the tail pipes, a little rich i know). I am at 6450ft of elevation (Rocky Mountains).

I know that mopars love a bit more advancement in the distributor, but i am still getting popping and back firing through the carb (probably ruined that power valve by now) but i have little to no throttle response at low speeds and then it occasionally stalls out. I cant even power brake the car without it stalling.

Which made me think that maybe, the carb is too much. If I remember, the 383s came with a 600 or 650 from the factory, at least for the ones who didnt have a 2 barrel.

Id love some input. Thanks.

 

[Kern Dog]

That is a really low idle vacuum reading. A stock cam should be producing well over 18" of vacuum.
The beauty of vacuum secondary carburetors is that they are on demand devices....they only give what the engine needs.
The 1980-89 318 4 barrels in Police cars were ThermoQuads and when Carter closed their doors, the GM Quadrajet was used. These are 800 cfm carburetors but the vacuum secondaries allowed them to operate just fine and pass strict emission testing.

 

[1STMP]

I have a 750 cfm holley on
a 366. Burns rubber for
half a block. 4200 ft
elevation. Your 74 jets seem
rather large, as I'm running
66's. The rule of thumb is to
drop 2 jet sizes per 2000 ft
of elevation from sea level
on sea level set set up
Holleys. Accelerator pump
cams also come into play
as your carb will need a
steeper delivery ramp. I use
a orange pump cam
mounted on hole position 1.
These are just rule of thumb
ballpark, but hopefully gets
you to narrowing down the
problems.

 

[4406bbl]

Almost sounds like a micky mouse valve job where they sank the valves and did not equalize the stem heights, so the valves do not close properly causing poor performance if it has a stock cam and lifters. Maybe do a compression test.

 

[4406bbl]

For the record, their is no such thing as too big of a carb if the motor is sharp. Ran an 850 on a single plane on a 340 with zero response issues.

 

[1STMP]

For the record, their is no such thing as too big of a carb if the motor is sharp. Ran an 850 on a single plane on a 340 with zero response issues.

No disrespect but,
were you on the beach at
Daytona, or in Denver
with their claimed mile high
status? (PS....Albuquerque
is higher than Denver). I set
my 750 cfm on the 366 @
6200 ft above sea level.
(Albuquerque)
Makes a huge difference for
carburetor response and
engine performance.

 

[Kern Dog]

You guys ever look at the CFM ratings of the 6 barrel/6 Pack setups? How about the dual quad Hemi?

 

[1STMP]

You guys ever look at the CFM ratings of the 6 barrel/6 Pack setups? How about the dual quad Hemi?

Thanks for the response KD.
Had a friend running a '69
Charger six pack in Roswell.
His carbs were set up for
an altitude of 4200 feet.
He was an avid dragracer.
He never changed the cfm
ratings of his carbs, only
jets and squirters to
compensate for altitude,
and a rough estimate for
ambient air temps and
humidity. His car (factory)
ran constantly in the 12's.
(1969 Dodge Charger 440
six pack factory stock)
He explained that CFM was
a good thing as it introduces
more air to the "pump" but
force feeding the "baby"
(fuel) makes them fat.
My guess, explained in his
simplest of terms.

 

[1STMP]

Almost sounds like a micky mouse valve job where they sank the valves and did not equalize the stem heights, so the valves do not close properly causing poor performance if it has a stock cam and lifters. Maybe do a compression test.

Sunk valves would make for
a very poor running engine
with audiable evidence.
Been there, done that.
I don't believe that is what
the OP is explaining in his
case.

 

[66 Sat]

I would say you have a tuning issue rather an over-carb situation.
Having really started learning the tuning side of carburetors in the last year or so, I'm appreciating how small differences can have a huge impact e.g added headers and car wouldn't run properly without backfiring. Upped the primary jets 2 sizes and it was fixed.
Now I'm playing around with an Edelbrock AVS2 650. Runs like a scalded cat on full throttle but is weak when loafing around and has a bog I'm struggling to get rid of. It's all in the tuning, and I'm no expert.
Watch some YouTube videos or better yet find an old school tuner to help. Get a vacuum gauge if you haven't got one and start playing around. Make the changes one at a time and write down what you are doing
I'm sort of enjoying the tuning process but even the weather has an impact so it's not easy.

 

[hunt2elk]

Get your timing dialed in (initial, advance rate, and total) before you even start messing with the carb. I would bet you need more initial.

 

[451Mopar]

You likely need at least 16 degrees initial timing.
I usually run a lower vacuum power valve at these high altitudes.
Make sure fuel pressure and float level are correct.

Now, the real stuff. Pull carb and check how much of the transition slot is exposed.
It's not unusual to have to drill the throttle plates to maintain idle while reducing the amount of exposed transition slot exposure.
Higher altitudes actually makes the idle circuit run leaner. Less air pressure in the carb bowl.
Usually have to increase the idle restriction size in the metering block, likely to at least 0.032"

 

[PurpleBeeper]

Hello all. So like the title says, how much carb is too much carb? It got me wondering if i have too big of a carb or i got something else going on.

I have a 69 sport satellite wagon. I pulled a 383/727 out of a 68 fury. It has a freshened upper end, but stock bottom end. I have an edlebrock torker intake and a rebuilt holley 4 barrel, single pumper carb. (3310-3 series, electric choke, vacuum secondary). I have gone through and verified that the points are set correctly (gapped and cleaned) and that the timing is set to 10 degrees (as per factory, for now). I have 12-13 inches of vacuum, i have size 74 jets in the carb with a 6.5 power valve, dont recall the squirters size, but i think they are a 38? I am running right close to 13.7 /13.9 air fuel ratio (as with a AF meter on the tail pipes, a little rich i know). I am at 6450ft of elevation (Rocky Mountains).

I know that mopars love a bit more advancement in the distributor, but i am still getting popping and back firing through the carb (probably ruined that power valve by now) but i have little to no throttle response at low speeds and then it occasionally stalls out. I cant even power brake the car without it stalling.

Which made me think that maybe, the carb is too much. If I remember, the 383s came with a 600 or 650 from the factory, at least for the ones who didnt have a 2 barrel.

Id love some input. Thanks.

View attachment 1615519

Your carb isn’t too big. Maybe a vacuum leak? Does the idle go pull-up & down? I suggest you put that carburetor back stock and adjust/modify from there as needed & I agree you need to advance your timing

 

[Don Frelier]

Ir could be a cam timing problem.

 

[Bluefish]

Ir could be a cam timing problem.

I agree. Retarded cam timing or ignition timing. After getting the carb mix screws set correct and i like to do it with a vac gauge. Turn them out 1/8 turn each til you get max vacuum in drive. I would start with the mix screws at 1.5 turns out. Make sure the pumps are set to immediately squirt as soon as you open the blades. After setting carb correctly, you still have same problem, look at the ignition timing and then the cam timing. I am assuming there are no vacuum leaks.

 

[Bee1971]

Honestly

GET RID OF THAT INTAKE MANIFOLD for your application

A nice dual plane will change everything in regards to LOW THROTTLE RESPONSE

Then we can start talking carburetors

 

[BSB67]

My guess is your problem is a little more than tuning adjustments.

I think we have way to little info to even start.

Did the motor run fine before you're "freshened upper end"?
What is the history of the motor before the freshened-up?
What was freshened and how?
What is new, used, or rebuilt?
What is the history of the carb?
What is your idle rpm when you get 12" of vacuum?
How does it idle when you are in gear?
How does the exhaust smell at an idle - does it burn your eyes?
When you cruise at say 40 mph, how does it run, what happens when you give it some throttle at that speed?
Is there anything it seem do do okay?

Your problem could be:
Something not right in the carb
Crossed or bad spark plug wire(s)
intake to head leak
carb to intake leak,
other vacuum leak

If the motor ran fine before - focus on the things you touched or did.

 

[Bee1971]

69 Sport Satellite Wagon

Boat of a car

"but i have little to no throttle response at low speeds and then it occasionally stalls out. I cant even power brake the car without it stalling."

6450 Elevation

Probably high gears



Single Plane Intake Manifold

 

[BSB67]

69 Sport Satellite Wagon

Boat of a car

"but i have little to no throttle response at low speeds and then it occasionally stalls out. I cant even power brake the car without it stalling."

6450 Elevation

Probably high gears



Single Plane Intake Manifold

Wait, this isnt answers to my questions, right?

 

[Bee1971]

NO

But he can answer all your questions and it still won’t matter