Carb Adjustment

Nick1966

Nick1966

Well-known member
(I am not a mechanic... at all - 1966 Ford Mustang 200ci, Auto)


Ok, so my poor Mustang failed inspection due to horrendous exhaust leak (84 decibels in cabin). I got it back from my mechanic with a new exhaust and it started a bit rough. I tried to find information on tuning the carb (Holley 1946) or making adjustment at least and couldn't find a dumbed down enough version. I hope one of you (guardian angels) has some experience with the Holley 1946.

There is a screw on the side which I understand is the idle adjustment. If I turn it too much the car will choke out. I played with it for a bit and if the car will start it will idle nicely. (Or at least nicer)

There is a large flat head screw looking piece on the front I think this is the choke. This is where my questions begin. I understand that as the weather changed I will need to play around with the choke. For instance:

The carb hasn't been adjusted since the beginning of winter. and was starting rough or not at all. Yesterday I closed the choke a bit (about an 8th turn) and the car started right up (85 degrees outside) and ran beautifully. This morning (about 20 degrees cooler outside, 65) the car wouldn't start.

So, when the weather is warmer do I want to choke closed more or open more?

How often should I adjust the idle?

How often should I adjust the choke?

Any information or advice is appreciated!
 
Emissions test for a 1966 car?

If it is warm, you probably won't need the choke. Little colder and you do. If everything is stock on your engine, to start the first time from cold, you 1) press the accelerator all the way to the floor. That sets the choke. Then you 2) press the accelerator HALF way down and crank it. If you already know that, never mind. A lot of guys are not familiar with non-EFI carburation.

There are three adjustments: 1) choke; 2) air/fuel mixture at idle; and 3) idle speed. If the engine starved out and stumbled, then ran better as you backed the screw out, that would be the idle a/f mixing screw. If it gets faster or slower, that is the idle speed.

Tighten the a/f screw until it stumbles. Then back it out until it levels out. Then give it another 1/4 twist. Idle speed should be 750 about **in drive**. You need a dwell tach for this, but they are cheap.

Choke is a different story. It is on the outside of the carb and you can only work on it for a short while until the engine gets hot. That should be adjusted to where it is no closer than 1/8" when engaged. It will open slowly as the engine gets warm. If it doesn't open, you need to clean all the linkages and make sure the pull-off is working properly. If the choke does not pull off, it will run rich and that will show up in your emissions reading as too much fuel. Make sure the engine is warm and the choke is all the way off when you have it tested the next time.
 
Ludwig to the rescue!

Thanks man I really appreciate that . I would normally put my foot down then crank it I didn't realize the second part of putting my foot half way. I will try that tonight.

I'm not sure where the third adjustment is located. I know where the choke is and the idle, i'll poke around and find the air fuel. I will pick up a Dwell Tach asap!

Thanks for all the info, I look forward to getting better at this
 
Your first link about the Holley 1946 (PDF) has the pictures that will show all the adjustment locations. Usually the choke is set up when a doing a rebuild, after that it would not need to be changed with the possible exception of coke cover due to a big change in weather (temp). Do all the settings if possible when for the choke when engine and air temp is cold. The idle mixture and idle RPM are set after the engine is warmed up good. :nod:
 
Listen to your Bubba.

The choke pull off is activated by a bimetal spring that expands when it warms up. This is located inside the black plastic cover on the side of the carb throat. A tube from the exhaust manifold leads up to it. What Bubba says about the choke pull-off being coked up means that there might be carbon from the exhaust getting sucked into the hot air tube and leaving deposits inside the choke cap. The problem is that the wall between #3 and #4 often burns though so, instead of warming hot air, it sucks in hot exhaust.

This has been covered here a couple times recently along with low-tech solutions. Use the search function for 'choke' or 'choke pull off' and you will find a couple strings covering the topic.

BTW, questions like yours give the old geezers here a warm shiver of pleasure, knowing that ONE MORE competent mechanic is now getting his long pants. There are no dumb questions. Sometimes there are dumb answers. Most of the guys here give helpful answers. If there is anything you don't get, just ask again for clarification.
 
Howdy Nick:

I've got a couple of questions; How come you have a Holley #1946 on your engine? This is a later carb designed to be used with a very different distributor/ignition system from the one used in '66.

How long has it been since this carb has been rebuilt. As with all carbs time and use, as well as lack of use, causes parts to deteriorate. Most likely to show up weak is the accelerator pump system. The symptom is a stumble on acceleration. To check to make sure the accelerator pump is pumping, remove the air cleaner, with the engine OFF, lever the choke valve open and look down into the throat of the carb. You might need a flash light. Now lever the throttle valve open. You should see a stream of gas squirting into the throat. If you see a stream, the accelerator pump is working. If you don't see a stream it is not working and is an indication that it might be time for a rebuild and cleaning.

Stumbling, inconsistant idle and stalling are also symptoms of a vacuum leak. Do a thorough check for any vacuum leaks around the base of the carb.

What distributor/Ignition system are you using. Many times carb problems are linked to ignition problems. What do your spark plugs look like? What is your initial advance setting? How long since an ignition tune-up.

Sorry to add to your list of things to consider just to fine tune your carb a little. But, as Murphy says, "It's never simple".

Good luck and keep us posted.

Adios, David
 
Last and final hint: BUY David's book. It is your one stop shop for tech help and ideas. Check the link on his sig.
 
CZLN6":22hgcq0k said:
I've got a couple of questions; How come you have a Holley #1946 on your engine? This is a later carb designed to be used with a very different distributor/ignition system from the one used in '66.
Click to expand...

About 10 years ago when I got the car I had to replace the carb. Mechanic chose that one. You can see it here:
https://www.facebook.com/media/set/?set ... 956&type=3


CZLN6":22hgcq0k said:
How long has it been since this carb has been rebuilt.
Click to expand...
8/2/2012 I rebuilt it

CZLN6":22hgcq0k said:
Stumbling, inconsistant idle and stalling are also symptoms of a vacuum leak. Do a thorough check for any vacuum leaks around the base of the carb.
Click to expand...
I thought we did that last week but I will check again, I remember it was loose.

CZLN6":22hgcq0k said:
What distributor/Ignition system are you using.
Click to expand...
Stock

CZLN6":22hgcq0k said:
Many times carb problems are linked to ignition problems. What do your spark plugs look like?
Click to expand...
Replace the last year (less than 500 miles)

CZLN6":22hgcq0k said:
What is your initial advance setting?
Click to expand...
I don't know what that means

CZLN6":22hgcq0k said:
How long since an ignition tune-up.
Click to expand...
Probably a while but I have recently replaced the coil, solenoid, replaced the points
 
I actually have the falcon six handbook but it's a bit more technical than I am able to fully understand
 
I have an automotive text book I try to read but by the time I get home from work i'm so tired I usually go to sleep. It's kinda the reason I ask here to much, because I have access at work....

The thing that really gets me is i'll research a topic for a while, ask questions then it's a five minute fix. -sigh-
 
HOwdy Back Nick:

Fyi; you have a miss match with your stock, Load-O-Matic distributor, designed for a carb with a Spark Control Valve in it, such as the stock 1966 Autolite 1100 carb and your current Holley #1946 carb designed for a DuraSpark II ignition system. THe DS II uses a ported vacuum signal which is what the 1946 carb has. Will this combo work- Yes, but not as well as either system is designed. The fix, or crutch is to fiddle with the initial advance setting of the distributor, and/or try a manifold vacuum advance source, or no vacuum advance at all.

The best/simple fix would be to upgrade to a later DuraSpark II ignition system that will be compatible with your Holley 1946 and it's ported vacuum source. The DS II ignition system includes the distributor, Module, coil and plug wires. It does away with points and adds mechanical/centrifugal advance. In all, it is more reliable, more efficient, and offers better performance and economy.

I was going to suggest that you purchase a Shop Manual for your vehicle, but that won't cover the '78 carb. Shop Manuals are a wealth of information.

Getting and learning to use a vacuum gauge and a timing light will be money and time well spent, if you're going to learn to tune your engine. Good luck.

Adios, David
 
I'll look into the vacuum and timing light soon but not right now. I want to see what I can accomplish with what I have. What I have is a Dwell Tach meter.

Now:

Adjusting the carb:
1. tighten idel screw (passenger side) until the engine stalls, back screw out 2.25 turns
2. adjust choke to 1/8" no more. Choke should no longer need adjustment until drastic climate change (winter, when the car will be garaged anyway)

RPM:
1. the engine must be warmed up
2. connect the positive lead (red) from the tach to the negative terminal of the coil
3. make sure tach it set to 6cy engine. The tach I have says rpm 10x so I need the screen to show me 50
4. adjust air fuel mixture screw (on back of 1946 carb) until desired rpm is achieve
5. drive car like I stole it (more baby it like I own it, more probable)


Does this sound correct? If not please explain? I would like to do this tomorrow morning (after mowing pops lawn, still not sure how I got roped into that...)


Thank you as always
 
Tune up specs in order

1. Set spark plug gap to .034
2. If you have a point type distributor Set the dwell to 39. Or a .025 gap
3. Set timing to 12 BTDC for an Auto Trans. 6 to 10 BTDC for a Manuel trans.
4. Set choke linkage adjustment screw on the index mark (high point) and choke cover on 1 or 2 Rich
5. Check choke blade is in the proper closed position start engine. Fast idle is set to 1200 RPM, next warm up engine when warm blimp the throttle so choke linkage moves off index mark to notched part of cam (ie so it's not holding throttle linkage open). Remove air cleaner lid to check that choke is now fully open, if it's open replace air cleaner lid.
6. Use the tach / dwell to adjust idle mixture to highest rpm then turn mixture screw in 1/4 turn (lean)
7. Set idle RPM to 525 or 575 with AC (and AC off) for Auto trans in drive with parking brake set. 600 to 650 RPM for a Manuel trans.
8. Repeat steps 6. & 7. To double check your mixture setting and reset your idle RPM and your done.

Good luck :nod:
 
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