Motorcraft 4100

[ol gray mare]

I just picked up a Motorcraft 4100 with the 1.08 venturi. It needs a rebuild. I researched the tag number, C6AF F, and the numbers indicate that it was from a 66 T-bird with a 390 or 428. I'm thinkin' the jetting is going to be too rich for my relatively stock 302. So my questions are: What would be the factory main jet # for the small block?
Also, for the secondary jets?

 

[vintage bronco]

what you have is a emission version for 390 not a good choice for a small block as the booster set up is all wrong what you need to work properly is a 4100 off a small block and they are pricy I have a 1.12 550cfm version off a 210hp 289 in a 64 Comet this is same as a 289 hipo carb only with a auto choke assy I will let go if interested it came off a running car but I would rebuild it just for the sake of fresh gaskets. I am not saying the one you have will not run but it will be a lot of work getting it dialed in.

 

[jckkys]

If the air bleeds and idle feed restrictions on the primary booster cluster are off, the ones on the 2100 booster cluster with 1.08 venturis, that was OE on 302s can be inserted on the primary side of your 4100. The jets should be close enough but I think the primary jets from your 2100, 47s I think, would also be right. You can run the secondaries a little rich. I think mine are 55s.

 

[matts460]

If jets/etc. has never been changed it will be fine. The 4100 is great old carb! AKA "cracker box". The 4100 were only on the base, non hipo 352,390 and 410,428 passenger car FE's and would not really be any more thirsty than the 302. The stock 302 probly wouldn't let the vacuum secondary open all the way anyway. The 4300 was the crapy emissions carb. Run fast from those! The 289 hipo 4100 is 600cfm I believe the other 4100's are 480cfm.

 

[jckkys]

Actually the large majority of 4100s were 1.12 venturi rated at 600 CFM. The 1.08 venturi version rated at 480 CFM weren't introduced until '64. For mild small blocks the 1.08 is preferable but far rarer. The 600 CFM was used on 428 police interceptors that had 427 solid lifter cams and put out more HP than 428 CJs. I owned one of these and a CJ . The PI out performed the CJ. Most of the so called 427 Cobras had 428 PI engines.

 

[ol gray mare]

I finally started the rebuild. When I disassembled it to put it in the carb cleaner, I noticed it has #48 jets in the primaries and secondaries. My further research indicated the small blocks came with 47 primary and 58 secondary on a manual trans. I think I'll try what I have first and fatten the secondary jets as needed.

 

[joshnjulie1]

Good to see others going after the tried and true. I swapped my Eddy 1406 for a 2100 (yeah I switched the intake) and could not be happier. The response from take off is AMAZING and runs SOOOOOOO much better.

 

[turbotim2]

I restored a 66 tbird with the 428, those came with the 1.12 venturi. The 1.08 was for small block mustangs and some other small blocks that came with 4bbls.

 

[ol gray mare]

Good to see others going after the tried and true. I swapped my Eddy 1406 for a 2100 (yeah I switched the intake) and could not be happier. The response from take off is AMAZING and runs SOOOOOOO much better.

I'm running the 1406 currently. I was tempted to return to stock, but thought I'd give this a try first. I know I got better mpg from the stock set up.

 

[jckkys]

I wouldn't be too concerned about the secondaries. A stock or near stock 302 will barely open the vacuum operated secondaries, if any at all. Added enrichment won't hurt anything tho. There were 1.08 4100s made for 289-428s and 1.12 venturi 4100s made for 289-428s. Holley made 450 CFM list 4548 replacement carbs for all the same engines. Any potential problem with the carb will be seen in a slight off idle stumble not at the top end where you rarely drive. Most carbs have this problem to one degree or another and the accelerator shot can be set up to cover it. Any 4100 is better than a 600 CFM Holley or AFB for a 302 either on road or off road.

 

[turbotim2]

You have probably already seen this but its a pretty good run down of the 4100 and its various uses over the years. I have one on the shelf that I am going to get professionally rebuilt one of these days. Until then, I will keep running my tried and true Autolite 2100.

http://mustangtek.com/4100/ford4100.html

 

[ol gray mare]

Good site! This one says it's from a "66 Ford, instead of T-bird like the site I found. I think that's a better ID #, because my carb is for a manual and I have never seen a '66 T-bird with a manual trans.

 

[turbotim2]

Ah yes, they did not offer a manual trans in the tbird in 66. It also looks like yours is not the CA smog carb, if I am reading that right. Either way, that 1.08 4100 is perfect for a 302!

 

[ol gray mare]

Well I got it running today! The best it has ran in years. The main difficulty I had was to resolve the base mounting between the manifold and base. This 4100 has a sealing ridge around the outside of the base which overhangs the manifold. I had a few adapters/spacers that eventually covered it. I ended up with 3 gaskets and 2 spacers, barely fits under the hood scoop. I'd like to do something a little less ghetto. Anyone have a recommendation for a spacer, part number, source?

 

[red hot71]

Summit has a summit branded 5/8" phoenic 4 hole spacer that I used for mine and worked with the manifold I had. Used the stock air cleaner with a K&N and 2" holes drilled around the housing.
I also was able to drill and epoxy in a tube for the PVC.

 

[ol gray mare]

Sweet, sounds what I'm looking for. Thanks, Jim

 

[ol gray mare]

Summit has a summit branded 5/8" phoenic 4 hole spacer that I used for mine and worked with the manifold I had. Used the stock air cleaner with a K&N and 2" holes drilled around the housing.
I also was able to drill and epoxy in a tube for the PVC.

The Summit spacer worked great!

 

[jckkys]

Sounds like you have a Performer intake. There are no problems with fit or leaks by simply using a Ford 4 bbl intake, carb spacer, and air cleaner. By now you can see that any 4100 works on a 302. I've found they all work on 351s too. The differences in calibration are small and I think they're at least as close to ideal as any universal Holley or AFB. Holley power valves and vacuum secondary springs work in the 4100s too, if you want to dial it in.