Patience with Autolite 4300 growing thin

JC Mustang

Founding Member
Nov 1, 2000
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Layton, UT
Finally got my new fuel sending unit squared away and could put on the "new" 4300 my buddy gave me. Once the fuel bowl finally got some gas in it, the engine fired up instantly with the classic one pump start. However, it quickly dies unless the gas is further pumped. After a while of working with it, I noticed that it has the (also classic) leak at the front of the fuel bowl. Since there is at least one stripped screw on this carb, I am becoming reluctant to bother rebuilding it, as I may just find it to be too much trouble.

I am considering ditching this carb and getting a 4100, my familiarity with the 2100 and the general good praise I have heard of the 4100 (and the denigration of the 4300) being the key factors. I am not concerned with "code correctness" (indeed there was no 4100 for 1968 Mustangs), but I do want a carb that actually works. In the picture of the bottom of the throttle body here, there seems to be a little vacuum fitting at the "front" of the carb below the thermostat housing. Is this for distributor vacuum advance? Do all the 4100s have vacuum advance? I need it. Also, are the 4100s from the Thunderbirds, Galaxies and such interchangeable here, at least functionality wise? I notice that the choke hot air fitting is pointing a different way on the Thunderbird pics at mustangtek.com.

I am reluctant to "lose" all the carb info in my 68 shop manual, would I set up my carb to specs in, say, the '66 manual? Any thoughts of any kind? 4300 defenders?
 
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2+2GT

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Apr 25, 2009
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Well, the 4300 can be retuned to work well, but the 1.08 4100 is somewhat larger, and IMHO, superior in any respect. A 1.08 from a 289 will work perfectly on your 302, If you have upgraded the cam, get a 1.12 that's been adjusted to work on the 289/302. Put your 4300 in a box for the day you want to show the car.
 

bnickel

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Aug 21, 2002
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the 4100 is a great carb, no doubt about it. i think for your application a 1.12 4100 from a 352 would work well. there was also a 4100 made in 68 and 69 for the 428 police interceptor engines and a few early 68 shelby's got it as well since they used the PI engine until the CJ came out later in 68. it also appears that the venturi clusters from one of the new Summit versions of the old holley 4010 carb will work on the 4100 as the spacing is all the same and they attach exactly the same as the 4100's venturi clusters, which could be a great tuning aid. i plan on trying this myself at some point.
 
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