Changing Intakes and Carb

5

55Merc

Junior Member
It’s been awhile since I posted but after many setbacks and unavoidable interruptions, I’m finally in the process of changing out the original “Teapot” setup on my ‘55 Mercury and replacing it with an ECZ-B and 4100 Autolite. Unbeknownst to me when I purchased the car (it wasn’t running) I found out later that the original Load-a-Matic had already been replaced with a ‘57 up distributor. Of course, when I got it running, it wouldn’t run correctly but I nursed it along for awhile while I started collecting parts. Long story short, the carb I have is a 4100 1.12 Venturi for a big block. 1.08’s are hard to come by but a guy on eBay is fabricating and selling bronze throat adaptors that press into the bores of the 1.12 4100’s to give them the same dimensions as a 1.08. You still have to re-jet the carb and do whatever else is necessary but after mods are completed, the 1.12 is supposed to perform like 1.08 carb for the cost of the barrel adapters ($20+$6 shipping or so) and jets.
https://www.ebay.com/itm/274639725910
 
You will be fine with the 4100 and 1.12" venturi's. It has vacuum secondaries, and they open based on engine demand (amount of air going thru the venturi's), so you won't over carburate on the '55 Merc 292.

Also if you want to go that way, there are lots of 1.08 4100's on EBAY.

Sal
 
I agree with Sal as I'm running a 1.12 on a 302 with no problems. I was told that a 1.12 was only 600 CFM. Is that true Sal?
 
The venturi restrictors will give the carb greater throttle response, especially at lower RPM tip-in (QUADRA-JET uses same principle). Same would apply to a 1.12. PONY CARBS used this approach as did FORD in their H4000 8V for street.

CFM (total rating) has not that much to do with it. It is what the engine can take in and exhaust.
 
scicala said:
You will be fine with the 4100 and 1.12" venturi's. It has vacuum secondaries, and they open based on engine demand (amount of air going thru the venturi's), so you won't over carburate on the '55 Merc 292.

Also if you want to go that way, there are lots of 1.08 4100's on EBAY.

Sal
Click to expand...

The 4100 was manufactured with both vacuum and mechanical secondaries. Mine is a C1AE-AH with mechanical secondaries which is what I wanted for the benefit of adjustment ability. I’ll be adding a PCV system that I will plumb from the valley pan to a nippled 1” phenolic carb spacer. Once I install the AOD ****** in the car, I’ll be experimenting with fuel mileage more than speed so re-jetting and the above referenced barrel inserts are just additional options to toy with.

The 1.08’s I’ve seen on eBay are infrequent and usually pretty expensive so the inserts are a fresh alternative. There’s just far more 1:12’s available because more big blocks came with 4 barrel carbs.
 
The 4100 was manufactured with both vacuum and mechanical secondaries. Mine is a C1AE-AH with mechanical secondaries
Click to expand...


Don't think I have ever seen a F4100 with mechanical secondaries. Do you have a photo?
 
I've been working on 4100 Autolite/Motorcraft carbs since I was 17, and never saw one with mechanical secondary's. Maybe it's something somebody rigged up. Like KULTULZ said, a photo would be great.

Sal
 
Back in the day the aftermarket used to sell a kit to convert your 4100 from vacuum to mechanical secondaries. It was just a metal piece that you installed on the choke side of the carb. It worked good. When I installed a Weiand 4v intake w/a 4100 carb on my Ranchero I made that piece for it. Maybe I can get a pic later of it.
 
SECONDARY MECHANICAL KIT DISCUSSION -

- https://www.tapatalk.com/groups/eds...chanical-secondaries-kit-holley-sp-t1809.html


454442
 

Attachments

  • CARB - 4100 Mech Secondary Kit.JPG
    CARB - 4100 Mech Secondary Kit.JPG
    34.2 KB · Views: 83
Last edited:
My bad, it was and is an aftermarket piece, I’m from “back in the day” myself and I guess I’ve seen enough converted 4100’s over the years to believe they were factory carbs. Anyway, I’ve read about the conversion kit before but didn’t give it much thought. I haven’t learned how to post photos yet so can’t provide one of mine. I may go with vacuum now anyway but still install the barrel reducers.
 
Yeah, I've seen those "trick set-ups" years ago. They didn't work very well as the accel pump wasn't rich enough, or timed well enough to have a smooth transition to 4 barrel operation. (read, bog) You can use Holley secondary springs to vary the opening on Autolites. A 1.12 carb isn't too big. Run 54 jets in the primary for starters. They will be close enough. Or maybe 52s might be more to your liking. This is farm tractor technology. I would be more concerned with the distributor timing, and curve. This is where the performance really is.
I have several 2150 Motorcraft 2 barrel carbs I have setup to use on a y-block. 1.21 venturi, electric chokes so you can plug the exhaust heat to the manifold, (always an issue) 54 main jets, brass floats, external vacuum break for the choke, water heated base plate under the carb, linkage fits, (usually) with no modification, extra vacuum ports on the carb for a CATV, a place to mount a step-up solenoid for A/C, etc. lots of performance gain. These things are much more "tune-able" than those old Autolite versions if I dare use that word. A very nice carb with 4 barrel performance, and look stock. (almost)
The only problem is, I still haven't got my machinist "friend" to fab me some adapter plates for under the carb.
 
Just remember that just because you have two 1.08s or two 1.12 carbs, with slightly different numbers, that they are not necessarily the same. Ran a 1.08 on my 302 with 4 speed and it was great. Put it on my 260 with an automatic and it ran rich just off idle and would bog when floored. Why, because it was for a 390 and the transition air/fuel mixture was richer for the 390. It bogged because the fuel from the accelerator pump was less restricted, giving the engine, fuel based on a 390 and no you could not adjust the linkage to compensate.
 
55Merc said:
My bad, it was and is an aftermarket piece, I’m from “back in the day” myself and I guess I’ve seen enough converted 4100’s over the years to believe they were factory carbs.

Anyway, I’ve read about the conversion kit before but didn’t give it much thought. I haven’t learned how to post photos yet so can’t provide one of mine. I may go with vacuum now anyway but still install the barrel reducers.
Click to expand...


No problem. It was a simple misnomer.

IMO, you will be much happier with the vacuum secondaries.
 
I have a pile of 4100's, never seen a kit to convert to mechanical secondary's. Have a few with mechanical chokes though. 289/271 hp hipo's used a 1.12 carb. I don't think you need the sleeves, you have them so use them, but think you should convert it back to vac secondary's.
 
Here's a couple pics of my mechanical secondary. The piece is about 2 1/2 in long and an inch wide. The large hole in the front hooks on the plastic stud on the end of the primary throttle shaft. The slotted hole is where the rod from the secondary vacuum lever goes. You can see a small screw/nut at the end of the slot. That's what opens the secondaries when the throttle reaches that point. That's how I set mine up. You can also see a small hole at the top of the piece. Your supposed to put a small pin (like a distributor gear pin) in that hole to open the secondaries. I found it works better the way it's set up now. I had bought one back in the 60's to go on my 56 Ford. Couple years ago I made this one from my fading memory.
 

Attachments

  • IMG_0156.jpg
    IMG_0156.jpg
    57.5 KB · Views: 13
  • IMG_0162.jpg
    IMG_0162.jpg
    44 KB · Views: 20
With that aftermarket mechanical secondary kit, you also lose having a fast idlse when on the choke. The lever on the carb that is pulling the secondaries open, is the lever that normally has the screw adjustment that hits the fast idle cam on the choke.
Probably why the carb pictured has all the choke parts removed. Good for warm weather I guess, but would have to warm up a little without a choke to idle decent.

Sal
 
The fast idle works just fine on my carb. You can install that piece without disconnecting anything on the choke. That's how the original piece was made. I don't know what the guy was thinking on the carb pictured. It's set up to open so late that the vacuum diaphragm would open it before he ever got to the point to open it mechanicaly. Never noticed a bog or hesitation on mine. Have a bit of the opposite. My "409" Ranchero will fry the tires before it bogs down.
 
You must log in or register to reply here.
Back
Top