Technical Automatic Choke Adjustment

I can also understand being burned out on trying to make flaky designed stuff work after it gets to be decades past it's design life, with no replacement parts available.

 

Automatic chokes, when perfectly adjusted, work fine ON STOCK ENGINES. Which is why I have posted about setting at a specific temperature. Often, a 60 year old coil has a bit of fatigue, and setting to the index setting of the shop manual will result in a lean setting. Ignoring the index setting, and setting by temperature eliminates this issue. And yes, for the fanatics, I have new old stock choke cover/coils for most 30's, 40's, 50's, and early 60's cars; but they are not cheap, and are generally not necessary. Why buy something expensive one doesn't need.

Most of my engines have been modified. One example would be my Pontiac with an aluminum flywheel and blocked heat cross-over (dumb for the street!). Would have to custom hand-wind a bi-metallic coil (yes, I do have the raw material to do so) to really slow the choke opening for city driving. The manual choke allows me to refrain from heel-and-toe at every stop sign for the first 30 minutes (and at my age, heel-and-toe is not as good as it once was). Pull the choke slightly at each stop sign, and then close it once again moving.

I just prefer the control.

The integral automatic choke does create issues for some folks that don't have a lot of carburetor experience in making sure the integral vacuum source is open (most have quite small passages, some with a couple of right angles).

First test I always use with an autochoke as long as still on the vehicle is to disconnect the heat tube at the choke housing, and hold a Kleenex tissue up to the housing. If the integral choke passage is open, then the Kleenex will stick, and on to other tests. If it doesn't stick, time to disassemble the carb and clean the passage.

In summary, not trying to talk anyone out of an automatic choke, but I personally prefer manual.

Jon

 

In the late 60's I worked for a Lincoln/Mercury dealer. We had an Eliminator One Cougar with a high performance 302 on the lot (new car). It had a Holley 4 bbl and a manual choke. The salesmen could not start that car and about once a week the battery was dead. If you operated the manual choke correctly, it started fine. The shop started using the car to do quick errands so that the sales people wouldn't run the battery down trying to start it.

The car was sold to a young lady in her early 20's and she had to be taught how to drive a stick. She never had a problem starting because she listened when she was being told the proper procedure. I only remember it coming back in for minor warranty work.

 

I'm sure a lot of the confusion about automatic chokes is due to the numerous variations in their design and operation.

For starters there are integrated chokes where the thermostat is directly attached to the carburetor. Then there are divorced chokes with the thermostat usually mounted to the intake manifold and a linkage rod connecting it to a lever on the choke valve.

Then there's the matter of supplying heat to the thermostat spring. With an integrated choke you can use air heated by exhaust gases (not the exhaust gas itself), with the heat coming from a tube plumbed into the exhaust stream thru a tube that runs thru the exhaust manifold.

Or with a divorced choke you can mount the choke t.stat in a well, or stove on the intake or the exhaust manifold. On a V-style engine you'll need to route some of your exhaust gas thru the intake manifold's exhaust cross-over passage. And to direct the exhaust there you'll need a heat-riser valve in one exhaust manifold outlet to partially restrict exhaust flow to force the heat from one side of the engine to the other through the cylinder heads. Simple, eh?

Of course with an integral choke you can also supply heat from the engine's coolant. Just route one of the heater hoses over to a bracket that mounts it right up snug next to the choke thermostat. And maybe add a little tin shield around it to help keep the heat in where it will do the most good.

Or in some cases the choke housing was cast with a passage that had coolant plumbed directly thru it to supply heat. Also adding potentially more coolant leaks.

But the most elegant solution would seem to be the electrically heated choke thermostat. In many cases they can be adapted to both integral and divorced choke applications. And in most instances they seem like the best alternative for HAMB-type vehicles that are fitted with headers (or manifolds) that have no heat-riser valve. And/or intake manifolds on V-engines that have a plugged heat cross-over passage.

 

This may not pertain to how to set a automatic choke but I have had many friends that said they do not have a choke and don’t need one. To me they have a carb idle mixture problem.
Both my sons race engine and mine have trouble when first started, when started we need to continue to throttle it to keep running until we get some heat.

 

Clay - guess it is my day to be disagreeable!

While I don't particularly like automatic chokes, I REALLY don't like electric automatic chokes! Really BAD experience with installing one on the wife's car (with an early powerglide). Too long to type here.

It is really not difficult to fabricate a heat stove to allow the use of the integral hot air choke on an A/M manifold without heat provisions. These used to be available, but doubt they are now. Here are instructions:

https://www.thecarburetorshop.com/Heatstovefabrication.htm

Jon

 

My dad had a 1978 ford courier that had a manual choke that would automatically go off after about 2 minutes

 

It would be pretty boring around here without the occasional disagreement, wouldn't it?


I've not updated a lot of vehicles with electric choke thermostats. But I have done a few using stats from similar, later model engine and carb combinations and had good results. Mainly just made sure that the thermo coil was wound in the right direction. Switched to an electric thermostat on my slant-six '64 Plymouth when I installed headers on it, for some reason.

Oh yeah, now I remember. I got them cheap from a co-worker!

 

Automatic chokes, fuckin new fangled shits. Wait, 34 Packard has an automatic choke, as I'm certain many other top tier cars back then did too. Nothing new under the sun. The Packards I've done never fail. 37 Cord had an electric automatic choke, but a manual override for colder climates. Pretty basic stuff if you like carbs.

 

Plugged tube?

 

How much different is the cap on that choke from an electric one?

I wonder if you could swap to an electric cap. It would still be automatic.

I will check my boxes for 1904's, to see if I have any extra caps. If I do have one, I will check it against later Holley and Edelbrock stuff.

 

While I was in HS, I started at a gas station that had 3 full time mechanics. I seemed to have the patience for dialing in those automatic chokes. Wasn't long after I started that I was adjusting most of them that came into the shop.

Plugged intake crossover tubes, or the bad stove pipe, or the vacuum leak or carbon build up for the hot air port or a defective external choke pull off was most of the causes for automatic chokes not to function properly. I removed a lot of manual choke conversions and made the automatic chokes work again.

 

Now, class... let's also thank Mr. carbking along with Mr. squirrel and all the other nice gentlemen who took time out of their busy day to come and speak with us today.

Class...

 

Now for the punks sleeping in the back of class.
Living in the south, on the 2 or 3 cold days Ive removed the air cleaner, wedge the choke closed with a screwdriver then crank. Remove screwdriver after cranking and let idle a few minutes.

but seriously, thanks for the info provided by the 2 professors
It’ll be utilized

 

The big difference is that the automatic choke measures engine heat, so will react differently in cold weather where the engine takes longer to come up to operating temperature. The electric choke measures time, and will pull off the same regardless of actual engine temperature.

Adjusting them to work in most conditions used to be harder when we drove these things in all weather. Now that I don’t drive anything with a carb in the winter, I can adjust it for normal nice day driving and be fine.

 

Actually, I think you've uncovered the reason why most, if not all vehicles with electric chokes tended to use that little flexible tube between the heat stove on the exhaust manifold and the bottom of the air cleaner snorkel.

During a cold start up it blocked the cold, outside air inlet of the snorkel and routed heated air up from around the exhaust manifold stove into the air cleaner. In that era the main goal was to get the choke open as soon as possible. This would help eliminate the "cold stumbles" while driving during engine warm-up as well as reduce the hydrocarbon emissions.

 

Back in the early 80's, my brother had a high mileage 70's F150. He was living in Minot N.D.. 50 miles south of Canada. It was mid winter & a cold front had things below zero for a few weeks. His truck would start & run ok, but when it warmed up it would stumble & load up real bad. I talked him through an automatic choke repair, a screwdriver, a hair dryer, some patience, nothing but de-icing the housing and reassembly. He then went to his favorite watering hole & his friends ask who fixed his truck. Well, my brother fixed it. Oh, when did he get into town ? He didn't , he fixed it over the phone.

 

This is, I hope it's understood, what I actually meant with my silly posts.
Good info. Good discussion.
Thank you.

 

Here's an early (33‐34) automatic choke. The mechanism is controlled by vacuum and heat, vacuum 1st. Note in the drawing below the little piston at the back of the internal lever arm. When the car starts thats your choke pull off and it's assisted by a counterweight on the opposite side of the choke shaft. It also shows the idle speed cam.


How it looks in practice, theres a thick metal disc screwed onto the ex manifold. That provides heat to the bimetal spring which is also assisted by the choke counterweight to take the choke out of play. The counterweight can't be seen but the spring housing and heat disc is pretty clear.

Climate adjustment is made by increasing or decreasing spring tension by rotating the round housing which is stamped "rich-lean" and direction. While this may have nothing to do with the topic car or use the functions and settings could be inspiring. Enjoy...

 

Thanks for the cool illustration of the Packard choke linkage.

At first glance it all looks a bit too "Rube Goldberg". But then you see that the at the upper end of the choke rod, where it attaches at the carb, the rod end is threaded and has a lock nut. Good lord!

Now it all takes on a more "Packard-y" vibe. At least as far as not just grabbing the slip-joint pliers and bending the choke rod to make a fractional adjustment. I mean, we aren't all just knuckle dragging Neanderthals after all!

 

I'll go you one better. Everything you said about an autochoke working fine as long as it's on a stock engine, but also running ORIGINAL fuel. Automatic carb chokes, through failure, differing fuel and inadjustment have spewed out FAR more pollution and wasted fuel than manual chokes ever would. I used to own a 1960 Falcon auto, and I prided myself on knowing exactly when to push the choke all the way in (remembering the summer and winter carb pump stroke lever holes as well, of course).

I have owned a Ford 302 auto with TQ since the early 70s - back then the autochoke worked perfectly on LEADED fuel (I'll admit the fast idle was, at 1500 rpm, a bit high when the temp hovered below 32F - but I never touched it - and it never fouled plugs either).

On the same car, with the same carb, each desecration of unleaded gas has meant the choke pull-off gap has become more and more unusable for immediate driveoffs without total plug fouling once the temp drops below 50F - meaning an extended warmup. As an old man, I am finally going to tweak it to get (a lot) more gap so I can jump in it once again to roar up the road from cold for a pack of cigarettes.

 

I've adjusted electric chokes the same way for decades, and never had one not work well. With the engine cold, I loosen the black housing screws, and turn the housing until the choke closes. Then turn it the opposite direction until it slightly opens. Lock the 3 screws down, and it's done. Seems to always work for various brands of carbs I've done.