1968 Need help with adjusting carburetor

[Jester]

I have what I believe is an Autolite carburetor on my c-code. It is hard to start the engine from cold and I usually need to try 5-7 times before it fires up. And then it usually dies a few times before it gets warm. I have also been told that the mixing is too lean and the engine needs more fuel. So I was thinking I need to adjust the mixing screws. Reading the instructions I got a bit confused so now to my questions:

Is it enough to screw the two mixing screws counter Clockwise or do I risk to effect other settings? must I also adjust curb idle speed? And is it true I need to have the car in gear and engine on when doing the adjustments? (Automatic) Why does this matter? Cant I adjust, then turn on engine and listen/check, turn of engine and adjust again? If I can not adjust the screws without removing the air filter this is what I need to do anyways or? Thanks for any help!

 

[franklinair]

I can give you basic information, but Rob Campbell is our resident expert.
Do you have a vacuum gage? Do you have an RPM gage?
1.) With engine OFF, and engine cold, check the choke butterfly to see if it is is almost closed. (I like to leave about a 1/8" gap from being fully closed..) Move the throttle a few times and see if the choke butterfly is almost closed. If the choke is not as I described, loosen the 3 screws on the automatic choke adjuster and turn it until the choke butterfly is as I described.
2.) Engine OFF. Screw the 2 bleeder screws all the way in (Clockwise) til they bottom out.
3.) Then back both screws out two full turns.
4.) Start the engine. Cold engine RPM should be 800RPM +/-. Vacuum should be 15 to 18 inches of vacuum.
5.) Let the engine come up to temperature. Increase the throttle RPM to see if the choke mechanisms allow the throttle position to return to the Idle RPM (about 600RPM+/-)
6.) If all is OK (hopefully) adjust the idle RPM to 500 to 600RPM, whichever sounds right to you. This is done with the transmission in PARK- NOT in gear.
7.) Adjust 1 air bleeder screw inward (clockwise) until the idle becomes rough and the vacuum gage goes lower. At that point, back the bleeder screw back out (CCW) 1/2 turn.
Now do the 2nd bleeder screw the same way.
8.) Re-adjust the idle RPM if necessary
Hope this helps.

Neil

PS
When the carb adjustments are done and the engine is happy, I like to check the ignition timing and adjust if necessary. Somewhere between 8 to 12 degrees advanced should be good. Then recheck your idle RPM and adjust to your liking. Not too high, and not too low. You'll be able to "feel" it when its right.

 

[dalorzo_f]

Very good overview.

A few links I had saved...

Here is some more info you can print out and refer to in the garage if you are old school and like paper...

http://www.carburetor-blog.com/motorcraft-2100-carburetor/

http://www.therangerstation.com/tech_library/pdf_documents/motorcraft_2150_carb.pdf

http://hurtle.com/cars/mustang/fixes/carb/

 

[Jester]

Thank you! Since I am new to the classic mustang game, bare with me and let me take it from the top step by step... regarding the choke, I guess the choke is engaging by turning the ignition key to on and pressing the gas pedal to the floor and then releasing? The choke is then controlled by what? Cooling water heat, exhaust heat? Someone told me to make it start easier I should repeat the pressing and releasing the gas pedal before starting three, four times. I thought this only controlled the choke and then I don't get why it needs to be repeated, it should close on first try. Does it control something else as well?

If I want to check the function of the choke butterfly/plate can I start and run the engine without the aircleaner or do I risk messing it up?

I don't have neither of the gages unfortunately. I was hoping I could adjust by just listening.

 

[Jester]

Thank you! Since I am new to the classic mustang game, bare with me and let me take it from the top step by step... regarding the choke, I guess the choke is engaging by turning the ignition key to on and pressing the gas pedal to the floor and then releasing? The choke is then controlled by what? Cooling water heat, exhaust heat? Someone told me to make it start easier I should repeat the pressing and releasing the gas pedal before starting three, four times. I thought this only controlled the choke and then I don't get why it needs to be repeated, it should close on first try. Does it control something else as well?

If I want to check the function of the choke butterfly/plate can I start and run the engine without the aircleaner or do I risk messing it up?

I don't have neither of the gages unfortunately. I was hoping I could adjust by just listening.

 

[franklinair]

It is quite OK to press the gas pedal 3 0r 4 times. (I do it, too) It's just to assure the carburetor choke linkages are activated, and gives a couple spurts of gas into the intake.
Chokes are operated by heat. When the engine is 'cold' the choke mechanism allows the choke to close. As the engine warms up, heat is transferred to the choke mechanism through the tube that is attached to the exhaust manifold (on the passenger's side of the car)and is attached to the "choke stove" (it is the black plastic device on the carburetor). The heat transfer warms up a spring mechanism, allowing the choke to open.
Sounds like you could use some assistance from someone more experienced, and has the gages to check engine status (vacuum, RPM gages and a timing light).

Neil

 

[x-codegtcs]

Jester - yes you can start the motor with the air filter and housing removed. It is almost impossible to make idle adjustments with the cleaner in place.

I would recommend reading Dalorzo_F's posts to understand the carb and how it works. The Autolite 2100 is a really good carb and should run well once adjusted correctly.

Once you understand the nuances of the 2100 carb, follow Neil's instructions step by step and it will get you a well adjusted carb (provided the jetting is correct for your altitude). Get the vacuum and RPM gauges - SO HANDY TO HAVE. As a lot of these old harmonic balancers are not 100% aligned as the rubber allows them to slip over time, I don't use a timing light anymore, I adjust the timing by the engine response . I have attached a highly recommended timing procedure for your reference.

 

[Jester]

Really appreciate the help! I've digested the info and will give it a go comming weekend, we'll see. Wish me luck!