I am using an Autolite 4100 in a 66 Mustang, 289 with a Ford cast iron dual plane intake. I have the exact primary and secondary jets that are specified in the shop manual for the car. These are size 48F primaries and 57F secondaries.

With most fuels containing ethanol, should these be changed? If so, any recommendation on size?

Also, does anyone sell booster venturies? My carb is not a C6ZF-B. It was a Ford replacement with the third digit a P versus the Z and it is a 1.08 version.

The carb runs good. Just thinking about some finer tuning.

Is the Carb Doctor the only place to get brass floats? Can the black nitril withstand the ethanol in gas?

Sorry for so many questions. Thanks.

As far as the 10% ethanol 90% gas mix (gasahol) is concerned no settings or jets need to be changed.

Sometimes I bump up the jets if the carb is going on a big CID engine though. Say if you have a 302 or 351. Or a variant stroker.

It seems to maintain a simmilar enough specific gravity and octane rating as to not cause problems.

No one sells booster venturis for the 4100 as far as I know. I have herd that boosters from a Holley 4010 fit and might work. Summit has reintroduced this carb and may have these for sale.

If your current carb and setup is working well I would not mess with it.

I have had no problem with either brass or nitrophil in gasahol.

Last time I checked you can get floats and other assorted parts at Napa yet.

Just make sure you get front and rear floats as they are different.

Ed Jenkins

Ford Galaxie Club of America member #3350
1966 Galaxie 500 Convertible built in Chicago Illinois, will have a stroker 390( 429 cid?). 780 Holley?, built C6, Crites Aluminum radiator, and a rust free frame from the south. Work continues.

Please visit and revisit the Carb Forum athttp://network54.com/forum/88781

I agree totally with Ed, the ethanol in todays fuel does not cause a problem with the Nitryl floats or the need for jetting, All it does is have a propensity to attract water and therfore extra problems when allowed to sit, It does break down gaskets faster as well ESPECIALLY when allowed to sit.
Good luck on boosters, I am not going to say no you won;t find them but better be prepared to talk someone out of them, anyone who knows what they are (and thats the only reason one would have them) will probably want a pretty penny for them. Incidently WHY do you need a booster?????

I do have a comment about your carb, and your post. From your post it sounds like you might be having some issues with tunability of your carb. That factory replacment carb that you have is not one of the best carbs out there, Although FORD used it as a factory replacment for ALL 4100's from 1966 thru the late 1970's, that carb was based on a 1966 Fairlane GT with a 390 motor and that carb is a california emmission carb for the FE. Ford kind-of figured that was the closest it could come to a generic 4100. For ford it was a smart decision at the time after all of all the four barrel carbs cars the vast majority were t-bird and galaxies (probably about 80-90%).
In todays world where a mustang guy is looking for a 4 barrel for his small block ford this is a really poor choice. Probably why you are having tunability issues.

Bill White
White Automotive