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Rebuild or replace?

  • Rebuild the 2100

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1966 289 3-speed
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Discussion Starter · #21 ·
Yes, it must close fully or you’ll have erratic function at best. It’s the only repeatable position to set it to. The spec in the shop manual that you use the drill bit to set is the “pull down clearance”. This will be where vacuum applied to the choke piston pulls the plate down to after startup. The way the shop manual describes it is very confusing. When you start the car, the choke should be fully closed, and the fast idle speed screw on the highest step of the cam. You should start at around 1500 RPMs...now, you don’t exactly want to put in gear at this speed and take off, so you give the throttle one tap, and the pull-down effect happens opening the choke a crack (approx. 1/8”...this is the drill-bit gauge setting). At this point, the fast idle speed screw should be on the second step marked with the sideways “V” indicator, and your idle speed will drop a step, say to 1,000 RPM. The shop manual makes this confusing, because they mention setting all this up in this position implying that this should be where your choke is set to when cold. That’s not the case, however, it is the position where both of those measurements correspond to each other. The problem is that if you don’t set to the fully closed position, you will never be on the high side of the cam and take full advantage of the fast idle function.
Thank you for this. Seems like I've gotten some conflicting info.
 

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Thank you for this. Seems like I've gotten some conflicting info.
With no thanks to Ford, this is a very poorly understood setup. It took me a long time to finally master it, and many guys give up long before they figure it out completely. I need to make a video as a public service to show the proper adjustment and function. It can be hard to put into words alone.

Outside of the confusing order of setting the fast idle and choke positions in the choke manual, they also fail to mention that the choke plate should be fully closed to engage the high step of the fast idle cam. They only mention that your choke housing should be set to one of the index marks, and they have a specification for that listed by application. This is presumably where the choke would have been fully closed with the provided spring when new. It's a totally unreliable way of setting them up now, because the springs have stretched, been changed, index marks missing, etc. Also, ambient temperature variations will affect the spring tension enough to make you need to change it periodically and adjust for different climates. Again, you want it to "just" close--meaning no cracks around the edges, but once it's closed, don't continue to crank it further, if you do that, the vacuum on the piston will be overcome by spring tension, and the pull-down position will not be reached until the engine warms up quite a bit. You will also likely starve the engine for air. You want to have the vacuum pull on the spring just a bit to affect the choke position and drop to the next step of the cam once you press the accelerator pedal after startup.

If you don't close it completely (i.e. if you set it to the drill-bit spacing), then your startup position will put the fast idle on the second step of the cam. This is how I once interpreted the shop-manual's description of the choke operation to be (I think a lot of other guys also have read it this way). I was never able to get great startups with that arrangement, and I noticed that in order to get the fast idle to approach the RPM specified by the book, I had to have my screw almost completely in at the end of its travel. I could also tell that the highest step of the cam had a curved surface with a clearly engineered step down to the "V" position, so I knew it was meant to be involved in the function, but wasn't with the choke set to slightly open. It was this fact that eventually made me realize I had been doing this wrong, and I deduced the correct way to do it. I now know that the shop manual was not deliberately confusing, they just omitted some details that would have clarified things for those of us working on stuff decades later.
 

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Discussion Starter · #23 ·
^ Thanks for the detailed explanation. So far it seems to be working for me as is (with the small gap). It started right up again this morning with no issues. The choke closed when I pressed the pedal and all functioned normally. Warm ambient temps may be helping but I'm going to leave it for now. Well see again on the drive home. Thanks again to everyone for the help.
 

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Just remember.... there is a big difference between a true carb "rebuild" and "hosing it off and installing a kit". If you didn't have to replace any Welch plugs you didn't do a rebuild.
COMPLETELY AGREE!!!!!!!!!!!!!!!!!!!!!!

I will add to that as well......Typically the carb rebuild "kits" are crap- either missing critical parts or the parts don't fit or are of poor quality. What I have done that has worked very well for me is to go to a carb rebuilding shop and ask them to put a "kit" together for me. The cost was around $50 but every part was there, fit correctly and worked!!!!

The other issue is many forget to take fine sand paper, laying the carburetor block on it side on a very, very hard flat surface and gently sanding the surface.....if it’s not flat/square/smooth, it's likely slightly warped...and although it looks fine is will develop a fuel or vacume leak and won't function correctly.

If you are comfortable with doing the rebuild yourself or have someone local who is and just need a good kit.... or you want to ship yours to them ...these guys have been around a very, very long time and are very good at what they do (this is where I buy my carb parts from)

Culver Carburetor Company
4921 Marine Ave
Lawndale, CA
310-679-2733 310-679-1616
 

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Discussion Starter · #25 ·
Ok. Well went on vacation and the car sat for 10 days. Tried to fire it up tonight and could barely get it to run. I saw the choke close when I pressed the gas but the fast idle wouldn't engage and it kept wanting to stall unless I gave it lots of gas. Even then the idle was very uneven as I held the pedal. After a couple minutes it wouldn't stay running without giving it gas so I shut it off. The choke had opened at that point. So I adjusted it some and manually made sure the fast idle was engaged but couldn't get a smooth idle with the choke open or closed. The car just seems to surge or miss even after adequate warming.

This is a video of what's going on. Note the last 20 seconds of the video after I kick the fast idle down. Seems like it's missing but I don't know what to make of this. Also please note the outside temp was 108 outside as this was happening lol.

 

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I'm not sure if we covered it in your other thread on the carb, but you need to adjust the bolt/screw in the plastic lever to make the fast idle screw rest on the fast-idle cam's highest notch in order to be on fast idle. If your choke is closing when cold, then you have to make sure that in this spot, the screw is on that high step. Then you'll need to adjust the fast-idle-speed screw (on the back of the carb--kind of hard to reach) in order to increase RPM to where you want it. It's basically a prop to keep your throttle slightly open, and that's how it works. It may be that the screw isn't turned in enough to make it run fast when choked and you're suffocating the engine on startup.

--and yes, the choke should always close when the engine is cold, regardless of ambient temps. That's where you have to adjust the position of the spring housing. The ideal setting is to turn it until it just closes completely, then it will begin dechoking as soon as you begin to warm the engine, and your fast idle will always engage to help you start the car.
^^THIS!!!!
 

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I still think your choke adjustment needs some finesse, but the surging idle is probably unrelated to the choke. Check your idle mixture screws again and all your ignition components, plug gap, timing, dwell. Another possibility is that your idle transfer circuit is partially plugged. If you can't tune that out with those things, I really think it's time to do the full rebuild on the carb.

A couple things I noticed from the video: The choke spring adjustment while the engine is running won't do anything for the idle speed (other than changing the amount of air let in). The reason is that the fast idle cam is trapped by the speed spring that's connected to the main throttle lever. Only after you open the throttle will the position of the fast idle cam be allowed to change. Again, it's best to think of it as a prop. Something like the box and stick trap that Wile E Coyote would set for the roadrunner. They are pinned against each other until something moves. You can reach down and push the cam down to lower the fast idle, but you can't lift it up without getting the screw out of the way by revving it slightly. If you rev it and then lift up on the fast idle cam, then let go of the throttle, it will keep the throttle slightly open to maintain the higher idle speed.

Also, don't forget your oil cap! ;)
 

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COMPLETELY AGREE!!!!!!!!!!!!!!!!!!!!!!

I will add to that as well......Typically the carb rebuild "kits" are crap- either missing critical parts or the parts don't fit or are of poor quality. What I have done that has worked very well for me is to go to a carb rebuilding shop and ask them to put a "kit" together for me. The cost was around $50 but every part was there, fit correctly and worked!!!!

The other issue is many forget to take fine sand paper, laying the carburetor block on it side on a very, very hard flat surface and gently sanding the surface.....if it’s not flat/square/smooth, it's likely slightly warped...and although it looks fine is will develop a fuel or vacume leak and won't function correctly.

If you are comfortable with doing the rebuild yourself or have someone local who is and just need a good kit.... or you want to ship yours to them ...these guys have been around a very, very long time and are very good at what they do (this is where I buy my carb parts from)

Culver Carburetor Company
4921 Marine Ave
Lawndale, CA
310-679-2733 310-679-1616
Aren't these guys out of business? The first number is definitely disconnected.
I haven't driven by there in awhile......
 

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Discussion Starter · #29 · (Edited)
I still think your choke adjustment needs some finesse, but the surging idle is probably unrelated to the choke. Check your idle mixture screws again and all your ignition components, plug gap, timing, dwell. Another possibility is that your idle transfer circuit is partially plugged. If you can't tune that out with those things, I really think it's time to do the full rebuild on the carb.

A couple things I noticed from the video: The choke spring adjustment while the engine is running won't do anything for the idle speed (other than changing the amount of air let in). The reason is that the fast idle cam is trapped by the speed spring that's connected to the main throttle lever. Only after you open the throttle will the position of the fast idle cam be allowed to change. Again, it's best to think of it as a prop. Something like the box and stick trap that Wile E Coyote would set for the roadrunner. They are pinned against each other until something moves. You can reach down and push the cam down to lower the fast idle, but you can't lift it up without getting the screw out of the way by revving it slightly. If you rev it and then lift up on the fast idle cam, then let go of the throttle, it will keep the throttle slightly open to maintain the higher idle speed.

Also, don't forget your oil cap! ;)
Thanks Kelly. Yeah I know the choke spring wont change idle speed and I understand its relation to the fast idle cam...that's not what I was trying for in the video. I was just checking to see if opening or closing the choke smoothed it out the idle at all which it didn't seem to.

However I believe the choke issues and surging idle are 2 different problem. Right now the surging idle has my main attention. I suspect its idle mixture. I have pertronix so no points to adjust. It was running quit well 2-3 weeks ago so I'm not going to check plug gap. I did have a bad coil plug wire that I replaced with a random one I had so that could be an issue. Can you tell me more about the idle transfer circuit? I'm not familiar.

Oh and the oil cap is connected to my air cleaner I find its much easier to take them off together when working on the carb ;)
 

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If you look at a carb from the bottom under the throttle blades, there are some pinpoint holes in the bores that allow vacuum to suck in fuel and air when the throttle blades are partially closed and you are on the idle circuit. When the throttle is totally closed, the transfer holes are above the blades and not exposed to vacuum, so they are inactive. When you crack open the throttle blades just a bit, you're letting more air in and need a tad more fuel to offset that before you are fully open and running off the main enrichment circuit and the venturi assemblies. So, there are a couple more small holes in the wall of the carb casting that additional fuel (and air) is drawn through. They are literally pinholes and can easily be plugged with dirt/varnish. Later carbs had a rectangular slot, but the older 2100s have tiny, tiny holes. These will affect your part throttle idle to an extent, so that's why I mentioned it. A small guitar string is a good way to clean them as well as using compressed air.

Another thought is your vacuum advance. It sounded like you were idling fairly fast in that video, and as such, you may be pulling some vacuum through the vac-advance canister. If your unit has a leaky diaphragm, you may be experiencing some surging due to timing being advance momentarily, then retarding again as vacuum is leaked. Not sure how recently that's been replaced, but to me that is a cheap and easy service item that should be replaced every so many years. You can infer this better by using a timing light and watching to see if the timing is jumpy like that. Of course, changes in RPM can make your mechanical timing jump too, so it's not a certain diagnosis. Anyway, something to consider.
 

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Aren't these guys out of business? The first number is definitely disconnected.
I haven't driven by there in awhile......
They have moved a couple of times....... the number on their ad shows... (310) 679-2733... everything seems to be still active
 

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Sounds like some ignition misfire going on there.... perhaps inductive crossfire between plug wires as they aren't properly run?
 

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Discussion Starter · #33 ·
Sounds like some ignition misfire going on there.... perhaps inductive crossfire between plug wires as they aren't properly run?
Now that you mention it, the PO had the plug wires zip tied together on both sides. I cut and undid the tie on the passenger side to give myself room to get to the choke tubes and remove the heat stack on manifold. If the wires are laying across each other is that really enough to cause that?
 

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Discussion Starter · #34 ·
Wow just did a google search and found tons of stuff about plug wires 7 and 8 causing inductive cross firing if you run them next to each other on 289's. Especially if you zip tie em...which is exactly how mine are run. I don't know if this is my problem but I'll definitely be re-routing my wires tonight. Thanks for educating me woodchuck!
 

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Discussion Starter · #35 · (Edited)
Got home and cut off the zip ties and rerouted the plug wires incase it was cross-firing ast Woodchuck suggested. Finally got the choke tubes installed so the choke system is complete. Fired it up and it started great with the choke and fast idle working this time. The idle was much smoother than last time, however there is still an intermittent surge about every 35-40 seconds at idle and a healthy one at that.

This is the most recent video of it running after I put it all back together. The surge is at 36 and 106 seconds. Really don't know what to make of it given how spaced out the surges are. Any ideas?
 

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No video, but what are the chances you have, potentially, some fuel contamination that is being occasionally being discharged through the carburetor? Have you pulled a fuel sample recently?
 

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Discussion Starter · #37 ·
No video, but what are the chances you have, potentially, some fuel contamination that is being occasionally being discharged through the carburetor? Have you pulled a fuel sample recently?
The video is up now. I have not checked the fuel and wouldn't know where to start. I can tell you that I have gone through about a tank and a half of gas since I've owned it. So kind doubt its contaminated fuel, but maybe a clogged filter?
 

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Discussion Starter · #38 ·
Anyone else have an idea on what's causing the surge in the latest vid?
 

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Doesn't sound like a surge to me. Sounds like it's cutting out for a second.
 

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Discussion Starter · #40 ·
Doesn't sound like a surge to me. Sounds like it's cutting out for a second.
My bad on the description. Any ideas on what to check? I'm kinda miffed given how far apart it happens.
 
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