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Automatic Choke Problems - 2 Barrel on 66 Mustang 289

11K views 31 replies 8 participants last post by  chasmalo 
#1 ·
Hi Guys,

I have a stock carburettor on a 66 Mustang running a 289. I for the first time attempted to do a choke adjustment to prep for winter in Australia (I live in Perth, Australia - not the coldest winter, kinda like LA). I opened up my carby and had a few surprises:

1. There is no piston.
2. It does not seem to be connected to the throttle at all. Pressing the accelerator on a cold start does not engage the choke.
3. It seems the choke was set on an always open position, the spring wasn't even closing it when cold.
4. The choke doesn't fully close when I try to close it by hand, even with the spring disengaged. I cannot figure out what's blocking it. Doesn't seem to be stuck (I sprayed carby cleaner) rather that something is stopping it from closing fully.
5. My guess is this is an Autolite 2100 but can someone please identify it.

The car still wasn't the worst starting cold, the problem was more obvious when I didn't drive for a week. I wonder what I should be aiming to fix! Below are pictures of the carby in its max closed position as well as the open spring housing with the missing piston.

Thanks guys!

Umang.
 

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#2 ·
Heya Umang, welcome to AFM!

It is an Autolite 2100 for sure. Just a few things:

First off, some people in warm climates seem to think an engine doesn't need a choke. A lot of them get disabled in various ways. It's not true, of course, but thankfully, 'warmup time' on a car where you live is going to be minimal, compared to a winter day here in Kansas for sure!

The linkage for the choke is really rather complicated, with a bunch of interlocking bits that both interfere or permit movement based on temp and throttle position. If the previous modifier person didn't monkey with other parts of the choke linkage, (and odds are he or she did not, because of the aforementioned complications). It may be challenging to find the right replacement piston for your particular carb. The spring should be easy, but I'm not sure the piston setup was the same for every year on that model. If you can look at the stampings on the driver's side front of the carb, I think you should be able to identify the year and model of your carb, and find the parts though. I suspect the 'won't close' thing is deliberate. If the spring arm inside the choke housing is just screwed on in the 'wrong' position, I think that would ensure the choke couldn't flop closed at random while driving around.

As for the 'not starting so easily after a week' part though, I suspect that's not a problem with the choke at all. Carbs are not like fuel injection, in that they require fuel in the bowl to run, and if left to sit, it tends to evaporate or even leak out through bad seals. If it's been a while since you last drove, you often have to crank the engine for a bit as the mechanical fuel pump refills the bowl. There is no magical fix to that, except to crank. Or, alternatively, if it really bugs you, you can install an electric fuel pump, which will fill the bowl without the engine turning over. IMHO, the old mechanical fuel pumps are very simple and reliable however, and often better than a cheap electric hanging somewhere awkwardly in the engine bay.

My advice? First figure out what model of 2100 you have, and then do some Google sleuthing to see if you can find just a replacement piston setup. If you can't, I'd look at Facebook marketplace or something similar, and just replace the whole carb, or buy one just for the piston itself. It's not uncommon to see them selling for as little as $75 here, though with shipping, it might be a bit more to you! Since most guys replace the manifold and carburetor with a 4V, these carbs are quite commonly available and not expensive. They work well, are super reliable, and with the exception of a few bits that tend to fall out and get lost, they are not tricky to rebuild. It's probably the best 2-barrel you could put on your engine.

Best wishes!
 
#3 ·
Hey Grimbrand! Thanks for the welcome and for the wealth of information!!

Thanks to this coronavirus, I have for the first time had the time to work on my car myself.

I checked the climate in Wichita and thankfully it's nothing like that here! My car has always lived in warm climate (LA, SF, Honolulu, Sydney and now Perth) so I guess it doesn't really need the choke. Even now it starts without the choke but still, I would like things to be like they were intended to be.

I am going to see my mechanic later this week and am now wondering if I should set my choke with the spring in a default fully open or partially closed position to avoid driving 10 miles with the choke closed.

And I just had another look at my carby and for the life of me I cannot understand what this arm and screw does - it does not seem to be attached to anything and just flops about loosely.
 

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#4 ·
That's part of the choke setup. It's all shown in the shop manual, I think, but mostly it limits things so that at WOT the choke plate will open slightly (if all the parts are there/attached). With pieces missing, yep, it's just a useless bit of dross. It also has to do with the fast idle, and helping the choke drop down to normal idle when you goose it after the spring's started to open things up. It seems overly complicated and sort of Rube-goldberg-esque, but it actually works pretty well until someone takes parts out!



Your car might run a bit rougher for a minute or two, but I agree - even in winter there, it should be driveable without a choke. Just be gentle and don't give it too much throttle right after starting, and you should be all right. So long as you understand what's going on, and don't just cuss at it like a millennial trying to drive a stickshift, you'll be good.


(and if you are a millennial who actually knows how to drive a stick, then you can laugh at the other millennials who don't. You just won the internet. *grin*)
 
#5 ·
Already searching for the missing parts to piece this thing back together!

I have been revving it when starting:surprise:just to make sure it doesn't stall. But I'll just let it settle and warm naturally now until it's all fixed. Will also see if the choke opens when it warms and if not will just open it completely till the choke is operational.

And yes I am a millenial! Though I learnt to drive a stickshift when I was 12 haha
 
#6 ·
If there is no thermostatic spring or heat riser from the exhaust manifold, then it for sure will not be opening on its own. You'll just have to set the choke plate 'wide open' (which it probably already is) and deal with it running rough on startup. You might have to baby it a bit when it kicks over, and mess with the throttle to keep it running. Don't rev it to the moon as the engine's cold, and still trying to get oil to the bearings when you first start it, but in the first few seconds it may want to cough and stall so just be patient. Sounds like you've already figured all that out though.



Getting it replaced should fix all the fuss.


Awesome to see that 'young people' love these cars and get to figure all this stuff out the same way we 'old people' did when they were a bit newer! I think you'll be surprised at the difference a properly working choke makes.
 
#8 ·
Thanks Guys - OK, so I do have a choke spring! Sorry, I didn't include it in the photos.

Yesterday morning (50 degrees) I set the choke to about 80% closed with the spring, so there was really no tension on the spring.

In the afternoon (70 degrees) I checked, choke still 80% closed, started the car, started and idled wonderfully! I let it idle for 10 mins, the choke didn't move at all (the heat pipe was connected to the exhaust). The fuel was definitely rich because there was some fuel splatter on the garage floor near the exhaust.

So I moved the spring to open it up completely before I went for a drive. I'm guessing the thermostatic spring is shot as well.

Car started well at night on the drive home (cold start, open choke, cool night). Some might say if it ain't broke don't fix it, but it will keep eating me up if I don't!!
 
#9 ·
There's actually a whole setup for drawing hot air up the heat pipe to the carb. If the passages are clogged (which is somewhat likely if that thing was open for a while) then there's no tiny vacuum leak to pull up the hot air and get the spring to move. The choke plate should be *closed* when the engine is cold. And by cold, I mean the coolant is at room temperature; it hasn't got too much to do with ambient air temp really. But just *barely* closed. The bimetallic spring will quickly open up the plate as the manifold vacuum draws hot air up the tube from the exhaust stove. There's also supposed to be a line going down to the stove, pulling filtered air from inside the carb's air filter, so that no dirt clogs up the steel wool down there on the exhaust manifold, or gets drawn up into the choke, but they often disappear, and it's not absolutely critical to operation.


Those thermostat springs just don't fail that often, unless they're all corroded or something weird.


If there's no piston, and no linkage, I would strongly advise you just adjust your choke to be 'wide open', because with the other bits missing, your car will still behave erratically or even stall. Better to put the spring in, and adjust the choke plate to zero restriction, and then let it warm up (engine coolant and block at operating temps). If your choke is closed after the engine warms up, it no longer needs fuel enrichment and all you'll do is foul your plugs, burn extra fuel, and burn a lot of gas. You don't want that.

It's also worth noting that the black sooty spatters you saw on the floor are probably just water with a strong fuel smell. Gasoline, when it burns cleanly, produces H20 vapor (steam!) and carbon dioxide. Of course, in the real world, you get some weird unburnt hydrocarbons, along with carbon monoxide, some nitrous oxides, along with soot and water. When the exhaust system's nice and hot, the water boils off and doesn't cause any problems. =)
 
#10 ·
True, so many things have been disconnected and open for a while, everything will need to be cleaned. When I first noticed it, the hot air pipe from the exhaust was actually disconnected from the pipe, i've put it back in but it's only held by gravity and a little bit of friction. Should I use some adhesive to ensure it doesn't come out?

Also, and unrelated and maybe ignorant question - the air filter intake tube (which rests on the front of the shock tower) has a secondary inlet from the exhaust. What is the reason for this?

Thanks again for sharing your knowledge! :smile:
 
#11 ·
If you mean the big pipe to the snout on your air cleaner, it's going to be pretty much useless to you. In places that actually get cold enough to freeze, the idea is when the engine is cold, your engine's literally breathing air right off the exhaust manifold. That helps prevent a condition called carb icing, where the fuel vaporization and low temps combined with low air pressure can make the carb so cold it gets covered in ice, and malfunctions. There's a spring loaded plate just inside the air cleaner snout that closes off the 'hot air' passage when things warm up, so it will breathe cooler air from the front of your engine compartment. It also helps your engine get up to operating temp a little faster, which in theory, helps reduce exhaust pollutants too.

Since you will never need 'hot air' for your carb where you live, functionally, it's fine to take off the shroud on your manifold, and disconnect that tube, unless you just want it to look completely factory stock. Oddly enough, the old 'snorkel' type factory air cleaners do pretty well compared to the 'high performance' type of open element round air cleaners though, maybe because they aren't just sucking hot air from right under the hood where all the heat rises while the engine's running.


And glad to help!
 
#12 ·
Man, I've learnt so much in the last 2 days!

That spring loaded plate has probably never opened in the last 54 years, I tried to force it open by hand it didn't budge!!

All these provisions for driving in cold weather, and my problems have always been related to driving in hot weather!!
 
#13 ·
The choke spring coil is a bimetallic strip which almost never fails unless the spring breaks...or someone throws it away. :) The system works by engine vacuum drawing hot air from the exhaust manifold through the choke spring housing. To keep the air clean is is not drawn in from the manifold but from the air cleaner instead; That is why there were TWO pipes connected to the manifold; air IN and air OUT. There was metal mesh inside the manifold cavity which may have rusted away. If so, the rust it formed will need to be blown out or else it will get in the choke housing and jam the small piston you don't now have. As mentioned, there are a lot of small passages involved. Its all explained in a Ford shop manual.

The snout on the air cleaner has a special air pickup from air on the outside of the exhaust manifold. The 'motor' in that snout is similar to the thermostat in your cooling system; its a wax pellet. That system is designed to keep inlet air to the carb at about 110F to help fuel vaporization.

https://www.allfordmustangs.com/forums/classic-tech/217734-intake-air-your-260-289-302-a.html
 
#14 ·
Just a thought here..... since most of the internals are missing, another option is to just make it a manual choke... just purchase a universal cable and run it from under the dash to the choke assembly.... you can set it up so that it will be 100% open unless you close it (partially) to start it and the remainder of the components to increase the idle I'm assuming you have... if not, they can be found or fabbed up very easily.
 
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#24 ·
I run an Edelbrock AFB on my old Pontiacs. I use a manual choke with a spring pull off. I pull the choke out to start and hold the choke while the car warms up to avoid a stall at idle speed. I release the choke and the spring pulls the choke open. That way I didn't have to remember to open the choke.
 
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#17 ·
I'm going to add some more thoughts. The throttle linkage looks really bad, worn parts, and just held together.



You need to find a set of carb overhaul instructions and do a complete adjustment of the outside linkages, cam screws, the plastic end nut at the choke, etc. I did not read one word of the step cam.



The choke coil spring is hard to understand how it really works. It can be put in backwards. It can be put in before, in the slot, and after the choke arm, only one is correct.



Get the linkages and spring right and that's most of the battle. The other stuff has their reasons for being, but these 2 are the most important.
 
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#20 ·
Hi All!

Just an update - I went and saw 2 mechanics and my local parts store the past few days. Both days were extremely cold starts (40 degrees F) and to be honest, the car started beautifully both days with the choke wide open.

The consensus from everyone was with the piston missing and the piston shaft hole not sealed, the spring just won't work. However, given how nicely car is starting, I am just going to use the spring to set the choke hard open with no give and let it warm up in the mornings. The trick is to drive her regularly!!

I'm going to add some more thoughts. The throttle linkage looks really bad, worn parts, and just held together.
Now this is another matter, pointed out by the parts store. Apparently the throttle spring is the wrong type, in the wrong place, a bracket is missing etc...

So I was wondering if anyone could please post a photo of their correct stock 2V Autolite throttle linkage so I can work out what needs to be fixed. Attached is a photo of my throttle linkage as it is now.

Cheers guys!

Umanng.
 

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#19 ·
I would think your estimated number of manual chokes is quite low. My first new car in 1971 came from the factory with a manual choke AND a manual throttle. Both are quite useful when needed. For the early Mustangs only the HiPo 289s came with a manual choke but that WAS a factory installed manual choke.

If you understand what its doing, and why, a manual choke can be a better approach. The automatic choke was so people didn't have to understand anything about chokes to drive a car. In those early days they also didn't work nearly as well as a well trained hand on a manual choke knob. With immense attention to emissions the manual choke went away entirely since doing it wrong only once would make your exhaust emissions over the legal limit.
 
#21 ·
Only the automatics used a dashpot so I assume yours is an automatic?

Except for the added cruise control servo (large silver and black cylinder in the lower right with a loose cable connected to the linkage) the attached photo is the factory setup for a March '66, 289, C4 car from Dearborn. Nearly all those linkage parts are available new. The shiny line above the cruise servo goes to the C4 modulator.

If yours starts and run well at 40F its running rich from something other than the choke. I doubt ours would run at 40 without a working choke.
 

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#22 ·
The missing piston will cause a vacuum leak. I don't know how serious but there is manifold vacuum going to it.

My first car was a Mercury Meteor with a '65 289 A-Code engine (Autolite 4bbl). It was a cold blooded creature but I live in Michigan where winters could be 32F (0C) or colder. It was a balancing act between too rich and too lean.

Don't rev the engine when cold especially after sitting for a while. It takes some time to get oil circulation and it's hard on the bearings.

CJM
 
#25 ·
1. Yes, it's an automatic. I'm not sure the dashpot does much, there really only 2mm of very light give in the spring button.
2. Thanks for the photo of your carby, really helps!
3. I reset the 2 fuel mixtures and hot idle screws (by ear) when the car was warm and with the choke hard opened (won't close when cold). So if it was running rich earlier, it should not do any more right? I'll report back as to how it starts cold now.
4. I left the fast idle screw untouched as with the choke out of the equation, it won't be doing anything anyway?
5. Should I check for a vacuum leak with a gauge on that draw hole in the carby?

Good to hear from a car-guy buddy in Australia or anywhere else!
Man, I like talking to you guys in America, you really know your cars and I like the American work ethic of knowing things in-depth and doing things well and with care. Also, vintage American cars are the best!!
 
#30 ·
5. Should I check for a vacuum leak with a gauge on that draw hole in the carby?
By 'draw hole' do you mean the vent hole in the little bump on top of the float bowl? If so, that is the air vent that allows atmospheric pressure air into the float bowl. You won't measure much of anything there but you also don't want to plug the hole either unless you are an adventurous sole like myself. The minute pressure/vacuum at that hole has a HUGE affect upon mixture. Most don't realize it but the size of that hole is definitely a part of the basic calibration of the carb.

Its a long story but if you thread a fitting into that hole and attach a hose to it then fractions of a psi into the hose will vary your fuel mixture from super lean to super rich. Making use of that fact is difficult if you don't have some good instrumentation. Otherwise, its best to leave the hole completely open. I spent months experimenting with that idea and decided the benefit was not worth the effort. Its an idea used on several aircraft carbs but getting the calibration correct is not a trivial task.

Speaking of Oz, I am probably one of the few on this forum who has booked a ride on the Indian Pacific passenger train; they actually wrote our names in a big 'book' before giving us the ticket. We didn't go far beyond Adelaide so we never got to Perth or even Western Australia but it was a memorable adventure. The dirt highway north from Port Augusta, the 'port road', was under water from a recent rain so we took the train to Woomera instead. :)
 
#26 ·
1) Dashpot only helps prevent stalls for automatic transmission cars when you snap the throttle closed at a dead stop. Honestly, some cars will stall, others won't. It just eases the plates closed instead of letting them fully shut instantly, and may or may not make a difference. Can't hurt.
3) Won't change anything about how it runs while out on the road, but will definitely improve idle when set right!
4) Good call - so long as the car's idle speed is where you want it anyway. Adjusting the idle speed down to something nice and slow can often be a dance between adjusting the air bleeds, then adjusting the idle speed screw. You want best vacuum/smoothest idle, and as you already know, only do this when the car's at full operating temp. If your idle speed is too high, your air bleeds become useless, as your carb will already be in the intermediate circuit. With an automatic, it'll lurch when you put it in gear, and probably stall a lot too, because RPMs are higher than your torque converter likes. Nice slow stable idle speed is good.
5) I wouldn't worry about it. The hole couldn't possibly be 'bigger than stock'. If it's plugged, then it might make you a *teensy* bit richer at idle, which would be compensated for when you adjusted your idle air bleed screws anyway. If it's wide open, well, that's how it would normally be anyway, and again - idle air bleeds get adjusted. Anything past idle is probably blowing through enough air that the tiny "leak" from this hole is virtually unnoticeable unless someone took a drill to the port. Which I'm sure they didn't.


Happy motoring, down there in the Land of Oz! (which is really kind of hilarious to me because I live in Kansas. Dorothy was my neighbor for years, and - no lie- my other neighbor had a dog named Toto too.) *grin*
 
#29 ·
Happy motoring, down there in the Land of Oz! (which is really kind of hilarious to me because I live in Kansas. Dorothy was my neighbor for years, and - no lie- my other neighbor had a dog named Toto too.) *grin*
One of my favourite films and my favourite band Aerosmith did a very heavily inspired Wizard of Oz song too - The Farm

Thanks again for the help man. We've had two gargantuan winter storms here this week. Monday it fines up again and I can check out my choke situation again.
 
#27 ·
Years ago when I first changed my '66 289 automatic trans from a 2- to 4-barrel I did not put the dashpot on it. I put one on after I had to take my foot off the gas pedal quickly and slam on the brakes to avoid an accident one day. The engine stalled and left me in a precarious situation. Luckily nothing bad happened.
 
#28 ·
Years ago when I first changed my '66 289 automatic <acronym title="transmission">trans</acronym> from a 2- to 4-barrel I did not put the dashpot on it. I put one on after I had to take my foot off the gas pedal quickly and slam on the brakes to avoid an accident one day. The engine stalled and left me in a precarious situation. Luckily nothing bad happened.
I like the idea of the dashpot and appreciate what it's supposed to do. (To me it looked like some kind of vacuum advance but it wasn't connected to anything, so I really wondered long and hard before looking at my service manual!!)

I think mine is worn to the point that it's not serving its intended purpose but my car doesn't stall if I suddenly take the foot off the pedal, so I'll leave this for another day.
 
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