[Found!] Carter Idle Adjuster Screw (for CAP Carb)

[Dana67Dart]

I have a Carter AFB 4305S (1967 Dodge 4bbl with "CAP") when I received it, it had a broken idle mixture screw. I successfully removed the broken part, and now need a replacement.

I looked on the web and can only find the more common 10-32 size adjustment screws

The type I need looks to be 1/4-36 (OD of threads is .2455 and tread count by thread gauge shows 36 Tpi) it has a necked down section near the needle end where the set screw limiter interferes. (curse you "CAP"!!!)

The needle portion is ~0.54" long and 0.08" at the widest part and ~0.04" at the tip. The threaded part is ~0.86"long. It is steel (not hardened) knurled on the end and uses a flat blade to adjust.

I suspect that other "CAP" Carter carbs might use the same adjuster maybe even 2bbl.

Non "CAP" carbs all seem to use a 10-32 adjuster

If you have any OR if you have a 1/4-36 non necked down adjuster let me know (I plan on not using the set screws and just plugging the holes)

 

[ch1ll]

that's an odd pitch for a 1/4 screw. are you sure that its not 6mm with a .75mm pitch?

 

[Dana67Dart]

that's an odd pitch for a 1/4 screw. are you sure that its not 6mm with a .75mm pitch?

I thought about that but didn't have a metric thread gauge so can't say for sure.

Why I think it is 1/4-36:

1. I measured the OD with a caliper and checked some thread charts and the OD is near the center of the range for 1/4" thread.

2. I used a thread gauge to measure for teeth and I agree 36 was an odd value but the gauge I used had 32,36,40 etc, 32 did not fit and 40 did not fit but 36 fit perfectly.

3. The carb is from 67 and while there were some metric dimensions used then (IE 14mm spark plugs) I have found few to no metric sized threads on my older american cars.

4. All the rest of the screws are standard and the adjusters for the non CAP carbs are called out to be 10-32.

I inquired from Mikes Carburetor Parts and his response was:

It is not close enough but has the thread size and pitch I believe it needs

I was going to buy a nut to check before I buy a tap and run it through the hole to be safe.

If I can't find a proper adjuster my alternative is to put a threaded insert into the larger hole using the set screw to keep it from rotating with 10-32 on the inside and use non CAP adjuster

 

[Dana67Dart]

I might have found a source, Thermoquad seems to have listed in an older Walker catalog an adjuster that looks like and has the correct thread size and pitch and the length is approx the same. It is part number 16-53 on page 71 of the catalog I found. Ill be looking into it tomorrow.

 

[4spdragtop]

I would be tempted to send broken screw to Mikes Carbs for him to id.

 

[ch1ll]

I haven't looked in machinery's hand book and I will but I have never heard of a 36 pitch 1/4 screw. but that does not mean there is no such animal. and I say this cause I'm a tool and die maker and I have tapped more holes than the average person ever see's in a lifetime. I would definitely proceed with caution. your idea of finding a nut like in a hardware store is a good idea. make sure you can turn it in with your fingers. any interference is not acceptable. good luck with your dilemma.

 

[Dana67Dart]

I have never heard of a 36 pitch 1/4 screw. but that does not mean there is no such animal.

Look at 16-53, this is from an old Walker ThermoQuad parts book.

 

[toolmanmike]

I couldn't imagine it being metric thread back in 67.

 

[RedFish]

I don't know if you could bush 1/4 to 3/16. It would hardly be a helicoil. I would sooner drill and tap the ID of the broken 1/4-36 I have to put 1/8 needle stem in it. Thread it in, braze it in, whatever.
If I had to clip one coil of the tension spring to consume a bit more of the 1/4 -36 threads I have available... so be it. I can adjust the length of my replacement stem accordingly.

 

[Dana67Dart]

Mikes Carbs for him to id.

I sent him a photo and dimensions and he came back with a mixture screw with correct threads but different pin. see post #3 above

 

[RedFish]

In looking again at your unbroken screw... Is there a boogered thread where this one was backed into the stop also? A damaged steel screw will back out while ruining the cast metal threads its in.
Even if the all the cast metal threads are still good, I would closely check and correct my screws. Grinding away a half round of boogered/off pitch thread can't do any harm.

 

[4spdragtop]

Looking at pics n dimensions isn't the same as "in your hand" inspection.
Good.luck

I sent him a photo and dimensions and he came back with a mixture screw with correct threads but different pin. see post #3 above

 

[Dana67Dart]

In looking again at your unbroken screw... Is there a boogered thread

I see what you are seeing. Ill have to look closely at it when I get home. the "Good" adjuster had the set screw screwed in when I received it. I unscrewed the set screw all the way and was able to remove the adjuster by hand. So if it is boogered it isn't too bad. last time I looked at it I did not notice anything wrong but I was mostly looking at the broken one

 

[RedFish]

So I went to the basement and studied over my identical 4305S adjust screws... I would need my buddy with a lathe and collet chucks to repair a broken one. Reason being... a new stem would need to be fairly well centered/straight and true. Although it doesn't operate water tight in the seat it'll likely get screwed all the way down there at some point. Don't want to feck up the seat.
I probably would put some effort in locate/purchase item # 16-140 from your chart above and deliver to him. Hell I might even buy the screw from post # 3 also to create 100% new screw. "Look here bud, this is the materials req'd and this is what I want done".
The only good thing about all this is the 36 TPI. What is really req'd in adjustment? 6 turns at most. A shorter spring does allow a shorter screw. So my replacement might show a 1/4 less outside the hole. It's fixed.

 

[Dana67Dart]

So I went to the basement and studied over my identical 4305S adjust screws

Want to part with an adjuster or two?

 

[RedFish]

Want to part with an adjuster or two?

Sorry.
I will mention this now incase you get to rebuilding... closely compare the height of the seats that come in your kit. I forget what brand first kit I purchased but the seats were taller. I like to have never fingered out what was amiss in my float height adjustment. Purchased a 2nd kit listed for the 4295 ( non CAP application ) to get a couple of correct pieces.

 

[Dana67Dart]

first kit I purchased but the seats were taller.

Thanks for the heads up. This is my first AFB and who know who did what to this carb before me. It had the choke completely removed. And unique "plugs" in the vacuum passage tubes

 

[hemi71x]

I guess i could sell you one of those adjustment screws out of my small stash of carb parts, if you haven't already got one.
hemi71x

 

[Dana67Dart]

I guess i could sell you one of those adjustment screws out of my small stash of carb parts, if you haven't already got one.
hemi71x

Sending PM

 

[Dana67Dart]

I'm still looking for an adjuster or two.

 

[Dana67Dart]

Well i found a local guy who had a parts carb with two adjusters. The needles are larger in dia but the rest is identical. They came off a 9000 series number carb. Im going to mark this thread as found. PM me if you want more info on what i found.