2 bbl carb

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ROB MCWILLIAMS

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I'm putting a new 2 bbl carburetor on my 273 65 barracuda, it has 2 adjustment screws on the front I'm guessing one is air & one is fuel...any recommendations on where to start with my air and fuel screws... I'm like a first grader walking in to 12th grade when it comes to carbs. I know and understand very little about them.. any advice would be great...
 
If both screws look the same both are idle screws. Adjust both out about 1 turn each to start. Be sure to adjust both the same.

Download your factory service manual from mymopar.com, and read up.
 
If both screws look the same both are idle screws. Adjust both out about 1 turn each to start. Be sure to adjust both the same.

Download your factory service manual from mymopar.com, and read up.
Make sure the butterflys open all the way.
 
They are both the same I'm almost positive... Hmmm never knew there would be 2 idle screws..
One for each barrel. most 4 barrels have 2 for the front barrels. (the primaries) Some performance carbs have 4 idle mixture screws. (4 corner idle)
 
They are both the same I'm almost positive... Hmmm never knew there would be 2 idle screws..

They are the idle circuit mixture screws for the amount of fuel you let in while idling.

The actual idle speed screw is over on the driver's side linkage area.
 
So when I'm being told that Mopar has a adjustment screw for the air and an adjustment screw for the fuel that's really just somebody blowing smoke up my *** huh...???? I've always been told that mopars are very finicky and hard to deal with. I have tried relentlessly turning one screw and not turning the other or turning both and have gotten absolutely nowhere I can get the card to run but barely and then other times it'll run but once I put a load on it it wants to bog down I admit I should probably just take it to a shop to somebody that knows what they're doing but I'm very stubborn I want to fix it myself QUOTE="toolmanmike, post: 1973122387, member: 2106"]One for each barrel. most 4 barrels have 2 for the front barrels. (the primaries) Some performance carbs have 4 idle mixture screws. (4 corner idle)[/QUOTE]
 
Sounds like some of the internal passages are plugged / gummed up. When you are adjusting the idle mixture screws and nothing happens, they are plugged.

First simple thing you can do is remove the idle mixture screws and spray carb cleaner in the holes, then blow the holes out with compressed air. Do this 3 to 4 times to allow some time for the carb cleaner to desolve the gasoline gum in the passages.

Reinstall the idle mixture screws and back them out 1 1/2 turns from the bottom of their threads.

Start up the car, let it warm up for 10 minutes. Have the car idling at around 700 rpm. Now adjust the idle mixture screws one at a time.

Slowly turn the screw in to close off the fuel until the engine starts to stumble, then back off the screw 1 full turn to let the fuel back in again. Do the same for the other screw too.

If you still get no response then the carb is plugged and needs to be dunked in a gallon of carb cleaner overnight.
 
A good carburetor is the life line to a good running engine.

Never have been a fan of the factory 40 year old 2 bbl carbs, they leak gas, stumble, and just plain don't perform very well, especially after 40 years.

I personally do the Edelbrock 1406 electric choke carb conversion to all of my 318 2 barrel setups.

Great running carb, plus it is a 4 barrel so you have the added performance of the secondaries to play with too. Starts so nice, performs very well, idles very well. Stock 318s with stock cams.

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Works for Me . . .
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then other times it'll run but once I put a load on it it wants to bog down


Let's assume for a moment that in this tune the engine idles well. The bogging down could be perception, your used to FI cars, it could be the advance curve, the vacuum advance is not functioning, or hooked to the wrong port.

I can not emphasize enough to get your cars factory service manual and start following what it says.
 
Initial timing could be out of adjustment, accelerator pump could be nfg too. Bogging off idle is often caused by a lean fuel condition.
 
That's pretty awesome I didn't know I could get an adapter to make a 2 bbl intake accept a 4 Barrell carb. I would love to have that on my car, just got to find a reasonable price carb...
A good carburetor is the life line to a good running engine.

Never have been a fan of the factory 40 year old 2 bbl carbs, they leak gas, stumble, and just plain don't perform very well, especially after 40 years.

I personally do the Edelbrock 1406 electric choke carb conversion to all of my 318 2 barrel setups.

Great running carb, plus it is a 4 barrel so you have the added performance of the secondaries to play with too. Starts so nice, performs very well, idles very well. Stock 318s with stock cams.

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Works for Me . . .
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That's pretty awesome I didn't know I could get an adapter to make a 2 bbl intake accept a 4 Barrell carb. I would love to have that on my car, just got to find a reasonable price carb...
I have picked up near new Edelbrock carbs for $100.
 
I’d like to know more about this too. Might make everything a little easier
 
So when I'm being told that Mopar has a adjustment screw for the air and an adjustment screw for the fuel that's really just somebody blowing smoke up my *** huh...????

Some carbs DID have an air adjustment. Older AFB 4bbls are one example, and not just on Mopars. They had one big screw "in the middle" that created an air leak, basically, to adjust idle speed, and then you would adjust the two idle mixture screws

Like this.........there is no mechanical idle speed screw (except maybe fast idle) there is the big one in the center (air) and the two fuel mixture, one on each side of it

Putting a 4bbl on a 2bbl manifold is more than silly and may compound your problem

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Sounds like some of the internal passages are plugged / gummed up. When you are adjusting the idle mixture screws and nothing happens, they are plugged.

First simple thing you can do is remove the idle mixture screws and spray carb cleaner in the holes, then blow the holes out with compressed air. Do this 3 to 4 times to allow some time for the carb cleaner to desolve the gasoline gum in the passages.

Reinstall the idle mixture screws and back them out 1 1/2 turns from the bottom of their threads.

Start up the car, let it warm up for 10 minutes. Have the car idling at around 700 rpm. Now adjust the idle mixture screws one at a time.

Slowly turn the screw in to close off the fuel until the engine starts to stumble, then back off the screw 1 full turn to let the fuel back in again. Do the same for the other screw too.

If you still get no response then the carb is plugged and needs to be dunked in a gallon of carb cleaner overnight.

I agree with pretty much all that's quoted here, EXCEPT, I usually try to get the engine to idle as slow as possible, then adjust the idle mixture, thus making the mixture adjustments most obvious. After adjusting mixture, set idle speed at best possible setting for your application.
 
I'm putting a new 2 bbl carburetor on my 273 65 barracuda, it has 2 adjustment screws on the front I'm guessing one is air & one is fuel...any recommendations on where to start with my air and fuel screws... I'm like a first grader walking in to 12th grade when it comes to carbs. I know and understand very little about them.. any advice would be great...

If it's a new carb,
then it is highly unlikely that BOTH idle-mixture circuits are bad. That leads me to think the fuel level is wrong or the idle timing is retarded.
So
by now, that carb is all messed up.
Remove it and drain it.
Make sure the choke blade is hanging vertical, and the fast-idle cam is disengaged. Fix the cam so it can't move.
Screw Both of the mixture screws all the way in until lightly seated; do not force them. Then back them out 2.5 turns. And leave them alone.
Flip the carb upside down. Go find the transfer slots, at the bottom (now top since it's upside down), of the bores, on the front side. They are the only matching slots one in each barrel, in there. Using the curb-idle screw on the drivers side, adjust the "speed" until the slots appear to be square. After this,leave them alone.
Ok put the carb back on. I'm gonna assume,for now, that the float level is ok. Hook the throttle back up and with it's throttle spring anchored. Do not hook up the Vcan. Instead, put the hose on the sparkport and plug it. Do not hook up the choke at this time.Make sure the choke blade is still hanging vertical, and the fast-idle cam is disengaged.
Now remember; Do NOT touch any screws !
Start the car and pull in some timing until she hits about 600 to 700 and let her warm up.
After she is warmed up,
Using timing; I want you to learn something. Pull in the timing a lot, watching the rpm go up up and up. Stop when the rpm stops rising. Now retard the timing until the engine wants to stall. You see how far that stinking distributor moves?! And the engine keeps on running. You can set your IDLE-timing anywhere in that range that you want to; I don't pay the spec book no mind.
OK, schools over;
now, using timing set the rpm to about 550/600. Then set the brakes and put her into gear. If it doesn't bang into gear, and the rpm is above 500, and it idles smoothly in Park,you are done; park it, kill it,and take a break.
But
If it does not idle smoothly;
DO NOT TWIDDLE ANY SCREWS OR TIMING.
Instead; Come back and report. If you do twiddle, you might have a hard time finding someone here to help you, cuz the first thing I'm gonna ask is; "did you twiddle anything?", lol. I have no way of proceeding if you changechit., and I don't want to be the guy chasing my tail.
If you do anything while waiting; let it be a valve adjustment, and followed by a compression test. Write the numbers down!, grasshopper,lol.
 
If you do anything while waiting; let it be a valve adjustment, and followed by a compression test. Write the numbers down!, grasshopper,lol
:popcorn:

Can't wait for the sequel! ,( Being serious, I have never tuned this way, interested in the full procedure)
 
There is/are a few ways to get to the same place. I chose this way cuz its fast, easy, and right on. The engine dictates it's own idle timing, based on the carb being used and where it's transfer slots begin.
The goal is for the engine to not have a tip-in hesitation, that is all. Using the mixture screws as trimmers you can get the engine to idle almost anywhere on the transfer slots.
But if the throttles are too low, then the transfers run the risk of drying up, and so when you tip the throttles in, she goes lean and probably stalls. As you increase the T-slot exposure, the tip-in progresses to a hesitation, a sag, and finally smooths out, then richer to where the mixture screws have to be closed up and then just plain fat at idle, going lean at tip-in cuz the screws have been shut off.
Starting with the T-slot exposure being square, and mixture screws a lil fat, takes most of the guess work out of getting the tip-in sag gone. But that just leaves the timing to set the speed with. And since the engine will idle on just about any idle-timing, the difference being mostly just speed, it's a natural.
 
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