Topic: adjusting Autolight 4100 4 barrel carb advice

[Mitchjd2]

Hello!
Can someone tell me how to tune my Autolight 4 barrel carb.  It's the original on my 289 "A"

Seems that it is running too rich as I am getting black powder on my exhaust tips and the "spitting" out of the tailpipes.
Also it is getting to where the engine wants to die at atop sighns.
Thanks in advance!

Mitch

[66GTKFB]

Go to the FAQ section of this portion of the forum. Glen (Soaring) has several links that should help.
Jim

[Soaring]

I would first check the timing to make sure the black smoke is not a timing issue before I blamed it on the 4100.  If you still think it's the 4100, then try adjusting your front idle adjustment screws on the bottom of the carb.  Turn then both all the way in, then out about 1 3/4 turns and keep turning out on both of them 1/4 turn with the engine running at a time until you get maximum idling performance.  If you still get black smoke after setting the timing and adjusting the idle screws, then you may have worn rings.  Just make sure it is black and not dark blue smoke.  Dark blue would indicate burning oil. 

[66GTKFB]

Golly gee Batman (oops, I mean Bat person - politically correct you know), I thought the screw on the right side of the base was for the right side venturi and the screw on the left side of the base was for the left side venturi. At least that's the way it is on my three 4100 carburetor equipped cars, and, son of a gun, the same applies to my 3100 Holley Bugspray two barrel carburetor on my VW.
Jim

[Soaring]

It depends on what you call left and right.  MOST folks call the right side of a carburetor by looking at it from the front of the engine, not from the driver's seat. 

[66GTKFB]

The right screw is for low idle and the left one is for higher speeds, but turn them both the same amount of turns. 

My right hand has always been on the right. Two idle screw are used to adjust idle, there's one on the right and one on the left venturis, not for high and low. No more long necks for you.
Jim
And I would remove the two screws to see if the taper is still straight, pointed and not grooved, and 1 1/2 turns to start.

[Soaring]

After I rebuild them, I start with 1 3/4 turns out, and it never fails that I will need to turn them out more than that for optimum performance.  You won't hurt anything by starting with 1 1/2, but that is just a waste of time. 
Anyway, let us know what you did to get that Mustang from smoking.  If you are dying at stop lights, it could be more of a problem than adjusting the carburetor.  I would rebuild the carburetor and set the timing, replace the spark plugs and wires, and if you have the points system still, either put in a new set of points and condenser or replace that old technology with a Pertronix system, then see how that puppy performs.  Yes, this stuff costs money, but nobody ever promised optimum performance from these old engines without proper maintenance. 

[Mitchjd2]

Hi Soaring. Thanks for the responses and thanks to Jim too. You guys are always a great help.

The mustang is not smoking.  It is spitting a little black liquid droplets out the back tail pipes on both sides.  Not much, but enough to see on the driveway.  It is also running kinda rough.  I haven't spent a lot of time on the engine yet as I'm doing the interior now.  The engine ran pretty good a few months ago when I bought it but seems to be deteriorating a bit.  I only drive it around the block a few times once a week.  I'm thinking it is just running rich.  I was hoping someone could tell me which of the 2 screws to turn to de-rich the fuel mixture a bit.  I'm a little scared of adjusting it to the point that it gets messed up. It's always safer to ask for advice before one puts a wrench or screw driver in their hand unless they are experts.

Mitch

[66GTKFB]

Running mixtures are controlled by internal jets. Idle mixture is controlled by the two screws at the base in the front of the carburetor and the adjustment screw on the left (drivers) side on the arm from the accelerator pedal. Get the car out on the open road for half an hour, then do adjustments.
Jim

[Soaring]

Mitch, the little bit of moisture you are seeing coming out the tailpipe is only condensation that builds up in the exhaust system during this time of the year.  All Mustangs haved basically sooty exhausts, so when you mix the natural soot with the natural condensation, you get that black drip from the tailpipe.  You also mention that you only drive it around the block.  That is a deadly practice.  When you take it out, take it for a long drive so that you get the engine and system up to a full operating temperature for a sustained period of time to burn off all that moisture which is the death of an exhaust system.