Rookie carb question...

[DarkRose]

Ok guys, I need some help.
I rebuilt the carb on my 79 Fairmont Futura, an Autolite 1bbl and it ran pretty decent, but horrible gas mileage. I did some adjusting and tinkering and such, and now when it runs, the gas mileage is MUCH better, but when I give it some gas, there's some hesitation before it "goes", unless I'm already running 50+ mph.

Here's my dumb newbie question, since I don't know much about these carbs at all, and have misplaced the tuning directions from the rebuild kit...

How can I tell a lean stumble from a rich bog? I'm not sure if I need to back the mixture screw out 1/4 turn again (I screwed it in 1/2 from when it was rebuilt...) Or if maybe the accelerator pump linkage needs adjusting, but to give it more gas or less?

Running an MSD Streetfire CD with Blaster 2 coil, new Motorcraft plugs at .050, and sometimes it seems a little cold natured and hard to start, sometimes it seems best to set the choke first, sometimes it starts right up without it...

I'm a little lost on this one, and wanna get it tweaked in a little better before it takes a trip to the body shop in a couple of weeks...

 

[ludwig]

Make sure your choke works dependably. It could be that the choke plate is not coming off. That can be handled with a cable choke or adjusting the pull off mechanism so it works properly.

If you already know how to adjust the idle air/fuel mix, never mind. If not, then with the motor idling properly in a warm condition (choke plate off), screw the idle mix down (clockwise) until the engine starts to stumble. Then back it off until it runs well and stop. That will approximate a good idle mix. If you are serious about this, get a vacuum gauge. They are only about $25 or so. Hook it up to manifold vacuum and back the screw off until you get the highest steady vacuum you can. Best case, this will be above 18*. Then give it one more quarter turn. This will eliminate a rich idle from your problem constellation.

You can also tune with the gauge by adjusting the distributor until you get max vacuum as well, with the vacuum advance disconnected and plugged at the engine. This will eliminate the advance issue.

If you are really ambitious, get a dwell tach and a timing light to adjust the timing dead on, by the numbers. THEN you can fool with the accelerator pump.

 

[MPGmustang]

the mixture screw only affects idle mixture, not running @ speed mixture for which you need a jet (i KNOW pony carbs has these jets for the autolite... what model?

generally the more out the screw is the richer the mixture (more gas) and screwin it in creates a leaner mixture.

your choke spring might not be set right, easy fix, loosen the black cover to the spring and twist it till the choke looses it's spring to stay closed, then slowly close it, keeping roughly 1/8th -3/16th inch before it's fully closed.

set the idle as strong as you can at the lowest rpm u can get, change the idle mixture to make it run the fastest it possibly can. then adjust idle setting to proper rpm (550-650)

honestly bog's are common on older tired carburators, it could be a loose throttle shaft or a bad acuator spring, or too small of a hole to dump gas when the pedal is floored. honestly I couldn't tell ya...

Good luck!
Richard

 

[mustang6]

For hesitation I look first at two things- one is the accelerator pump action of carb, the other is distributor timing. For the accelerator pump test, run the engine to make sure the carb is full of fuel then shut off the engine. Take off the air cleaner, look down the carb throat, depress the throttle quickly- you should see a decent fuel squirt from the pump. If not, something is wrong in the carb. To check the timing you really need a timing light to see if your timing is correct, and if it is I would recommend advancing up up 6 degrees over stock. The further advanced the timing, generally the less bog or hesitation it will have when the accelerator pump squirts the gas shot. Idle speed will also typically increase when you advance the timing, you can slow that back down with adjustments at the carb.

 

[JackFish]

On the Holley 1946 there is a rod on the front with a u-shaped bend.
You need to squeeze that u smaller.
This will give a longer pump stroke.
Some trial and error will be involved.

 

[CZLN6]

Howdy Dark rose and all:

I'm confused. Did you say that you have an Autolite carb on a '79 Futura? The last use of the Autolite 1100 was 1969. Please check and verify that you are using an Autolite carb. IF so, what Autolite? The correct carb for a '79 200 is a Carter YF. Is this a manual trans or auto combo?

Don't worry about the lean or rich until you have the choke functioning correctly and as lean as possible, the initial advance set and the low speed air screw optimized.

Keep it coming.

Adios, David

 

[DarkRose]

Howdy Dark rose and all:

I'm confused. Did you say that you have an Autolite carb on a '79 Futura? The last use of the Autolite 1100 was 1969. Please check and verify that you are using an Autolite carb. IF so, what Autolite? The correct carb for a '79 200 is a Carter YF. Is this a manual trans or auto combo?

Don't worry about the lean or rich until you have the choke functioning correctly and as lean as possible, the initial advance set and the low speed air screw optimized.

Keep it coming.

Adios, David

I have no idea why it didn't post my reply earlier...

@CZLN6 - I have no clue why I said Autolite, it's actually the Holley 1946 1-bbl (Motorcraft tag, don't have the codes in front of me) all rebuilt with new electric choke.

Automatic, not sure if it's a C3 or C4... I've not got under it to check pan shape yet, will do that soon with an oil change, and probably tranny fluid and filter change.

Have had the timing gun on it, 10º BTDC @idle, w/o vaccum...

@mustang6 - You're saying I could move the timing to as much as 4º BTDC?

 

[JackFish]

You should be good to go at 10°.
Like I said, adjust the accelerator shot with the rod on the front.
A smaller bend gives a larger pump shot.
Factory setting is about 1/4 or less of the actual travel available on the stroke.
It was set to minimal due to economy concerns of the era.

 

[CZLN6]

Howdy Back Dark Rose and All:

The good news is that the Holley #1946 didn't generally appear until the 1980 model year, but with FoMoCo who knows. The other good news is that earlier versions of the #1946 still retained some adjustability; Low speed air screw, accelerator pump rod. The accelerator pump system is weak. Later versions have the air screw sealed and are much more EPA crutched. If I recall correctly, the stock initial advance setting for a '79 200 with an auto trans is 10 degrees BTDC (but check you emissions decal under the hood to be sure. You could try as much as 15 degrees ( 5 over specs) and see how it works. But first take Mustang6's suggestion and peer down the carb throat to see if the accelerator pump is able to squirt. If no squirt, you've found your hesitation cause.

The other good news with a '79 model 200 is that they typically don't have the quick burn cat attached to the exhaust manifold. But since your engine has a #1946 Holley you may not be so lucky.

Adios, David