Any Carter carb experts here?

[NutmegCT]

1958 Rambler six with Carter YF carb and automatic (manifold heat) choke.

Engine starts and runs beautifully when warm; idle speed about 550 rpm. But when starting cold, engine dies unless you slightly hold the throttle open. Carb adjustments are (1) idle mixture, and (2) idle speed.


Here's the situation:

Cold engine.


Stab and release gas pedal to set choke.


Ignition on - crank - engine fires immediately.


Very lumpy, fires about twice every second, then engine dies.


Restart several times without touching pedal - same result. Engine dies.


Slightly open throttle and crank - engine doesn't die. Continues firing slow but then smooths out and increases speed. But release throttle before about two minutes have passed, and engine dies.


Restart and hold throttle slightly open for about five minutes, release pedal and engine fires smoothly and idles normally at 550. In other words, you have to manually hold the throttle slightly open for about five minutes until engine is warm - then you can release the gas pedal.


Punching gas pedal at cold definitely closes the choke butterfly. As engine warms, choke butterfly slowly opens.


Opened choke, cleaned out, verified all parts are free. Internal choke arm seems (?) properly engaging throttle extension tangs. Carb is clean. Mixture and idle set properly for warm engine.


Only way to prevent the problem completely is to raise the idle speed (turning in the idle screw) several full turns. But then the warm idle is about 1200 rpm.


New points and condenser, clean fuel, rebuilt carb, timing correct, new plugs, etc. Car runs great when warm. The automatic choke definitely closes the choke plate, but doesn't seem to raise the idle speed.

Attached: diagram of choke.


What am I missing?


OK - back to my egg nog. Thanks.
Tom M.

 

[pdplot]

Sounds like mixture is too lean to burn at cold idle. Perhaps there's some way to measure the fuel/air mixture. Beyond my meager expertise.

 

[3798j]

I'm certainly no expert on Carter carburetors, but I've lived with one (Carter AFB) for 29 years. It has virtually the same choke actuation linkage as the YF. Instructions call for bending the arm of the rod to increase or decrease the throttle opening when choke is actuated. There are those that will say the term "sticking choke" started to be widely used when this automatic choke first came about. There are also those that will tell you you need four arms....one bent correctly for the four seasons of the year. Finally there are those that will convince you that the only way to proper choke idle speed (and sanity) is to replace the automatic choke with a manual conversion (Dorman has one). With my AFB, I've got it working acceptably for cold starts in mild or hot temperatures. Set up that way, it will not start, let alone idle, without foot on gas pedal in cold weather.

 

[LarryK]

These Carbs seem to need choke adjusted for every weather (temp) change. I believe the fuel of today is the problem. My 77 Ford RV with a 460 and FoMoCo Crab is the same way. Have to adjust 2-3 times a year as wife will not tolerate a manual choke. Last manual she used was in her GT6.

 

[NutmegCT]

Larry - what's the adjustment you do? I'm thinking the opening of the choke butterfly needs to be changed - but I'm just stabbing in the dark.

I can't see Carter saying you have to "bend that fast idle rod" each time the seasons change. But I can see just turning that black choke cover - which changes the choke butterfly opening. And more air would give a faster idle to start the engine.

Thanks.
Tom M.

 

[LarryK]

I would adjust black choke cover. I have to readjust mine from summer to fall to winter. I know of guys who take their Cobras and Mustangs to a shop on a regular basis for this. I have done this for years on all makes. Is not just the Carter, but Holley, Ford and Rochester too. All you can do is move a slot at a time, let cool and do it again until you find the sweet spot. Might make note of what mark you are on at what time of year. I mark mine with paint, red, green, yellow, so all Inhave to do is know the temp for the season and move it.

 

[NutmegCT]

Success! I rotated the black cover, and watched the choke plate open up a bit.

Engine was still cold from last night, so I cranked it and it started immediately, then actually continued to (slowly) idle. Didn't die. I watched the plate slowly open to full vertical as the engine warmed.

Jeez - would have saved some headaches if there were a Carter "Adjust your choke" manual somewhere. I've seen some online references which say to set the cover pointer one notch beyond the index point - but no explanation of why, or when to change the setting.

Thanks Larry.
Tom M.

 

[3798j]

Counter clock wise makes it leaner. You can see I'm two notches lean from the index line (that I think doesn't exist on the YF).

 

[3798j]

And here's about the bending instructions...although this is for the Carter 4bl:

 

[3798j]

More on bending: https://www.autozone.com/repairguid...rter-YF-1-BBL-Carburetor/_/P-0900c152801db33b

 

[NutmegCT]

I discovered that rotating the choke adjustment cover, or bending the rod, didn't do what I need. Here's the issue:

Cold engine - setting the choke does *not* change the idle speed. Punching the gas pedal once sets the choke plate closed perfectly; choke plate opens gradually as manifold temp increases.

But - the idle speed linkage (the "hook" at the left) never changes, regardless of choke mechanism, setting the choke, or otherwise. The "hook" moves exactly in tandem with the throttle linkage. Only way to keep the engine running when cold is to hold the gas pedal slightly down.

See photos. You see the choke throttle linkage (the "hook") in raised to full open and released to full closed position. But I can't see anything in the choke mechanism to actually "lock" that hook into a fast idle position. The "fast idle cam" is present - but no part of the cam touches or interacts with the throttle linkage "hook" in any choke plate position.

Hook up (throttle wide open):

View attachment 40959

Hook back down (warm idle position)

View attachment 40960

I removed the "unloader arm" to show the fast idle cam. There's got to be some setting or adjustment I'm missing. I've got several Carter YF manuals, but none talk about how to position the fast idle cam (and unloader arm) in relation to that throttle "hook". (Warm engine runs and idles perfectly.)

grumble grumble

 

[3798j]

Found this instruction for setting the YF's fast idle adjustment (although it looks as if its showing one with a manual choke, think lip should still contact that boss on one with auto-choke...worth a try anyway). Not exactly like my AFB, but it is a similar set up.
"With the choke held open in the wide open position, the lip J should contact the boss on the throttle body.
Adjust by bending the fast idle rod at point K."

 

[NutmegCT]

Thanks Jay. I must be dense, but how do I know when I've "bent" that rod correctly? I've seen various references to holding the choke plate open, and bending the rod - but what difference(s) in what part(s) am I looking for?

Could you point me to the page with all the text instructions?

Tom M.

 

[3798j]

Tom, Look at the last drawing I posted...specifically Tab "J"...it's a little "hook". That should be in contact with the carb body when the choke is open (how I would describe it...It's gotta be resting against it when the choke is open). If its not, bend the rod so that the tab comes in contact with the carb body.

 

[NutmegCT]

Thanks Jay. Take a look at this diagram of my YF carb:

https://www.britishcarforum.com/bcf/attachment.php?attachmentid=40476&d=1451061495

Note the different linkage setup. There's no "stop" for the idle linkage to rest on. One set of instructions I found says to remove the carb, then stick a drill bit up to slightly open the main butterfly, then "bend" the linkage arm. But I don't know what I should be seeing when I bend it. If I put the drill bit up there, how much, and in what direction, do I bend the rod? Am I bending the rod so that the drill bit slides up with no resistance? In other words, so that the bit isn't needed to hold open the butterfly?

 

[3798j]

Tom, I'm screwing you up showing that photo of the YF with a manual choke. Sorry. Tomorrow morning I'll get out to the garage and see if my manual on the afb can shed some light as to what direction will increase fast idle.

 

[NutmegCT]

Jay - take your time, no rush. I have some snow to clear!

It's not just "what direction to bend the rod". It's that to insert the drill bit into the throat per instructions, the carb has to be off the car. So I'm just guessing when I bend it, as there's no way to check idle speed if the carb is off the car. Every attempt, I have to put the whole thing back on the car, and test the cold start idle speed. If not right, have to remove the carb and do it all again. Seems unusually clumsy!

Thanks!
Tom M.

 

[3798j]

Tom I figured out where I've gone wrong trying to help. The Carter YF with manual choke has an exposed rod that can be adjusted (bent) to raise or lower the fast idle speed. Looking at on-line photos, the auto-choke models don't. The Carter AFB that I'm familiar with has on the opposite side from the auto-choke an exposed rod and cam that controls fast idle speed. The cam has an index line that is to line up with an adjustment screw. This alignment is done by bending the rod. I mistakenly thought that while your carb didn't have a fast idle adjustment screw, it had a rod that could be adjusted (by bending) to increase or decrease engine speed. This is a photo of that fast idle rod and cam that's in my car:



My apologies for trying to have you adjust something your carburetor doesn't have. I'm very sorry. The mystery remains....how can the fast idle be raised on a Carter YF with auto-choke?

 

[NutmegCT]

Jay - certainly no apologies needed!

I very much appreciate your suggestions, and every bit of detail helps in my carburetor adventure.

Say, what car do you have with a Carter AFB?

Tom M.

 

[3798j]

'64 Corvette
Tom...here's more on choke housing adjustment...just don't know that it'll raise engine speed.
https://1bad6t.com/Maverick/repair/fuel_system_05.html