I know the mods may move it or delete (and that's ok) but here is an add that may be of interest. Just want to get it to this group. Are these rare or is this part legit?

http://buffalo.craigslist.org/pts/1333487877.html

I've read about those carbs way back in the 80's reading HOTROD from the 60's. Don't recall if they were only used on Motion cars but doubt it. Maybe just a poor seller for Holley???

Motion did use the Holley 3BB on some of their Phase III conversions in the 60s -70s.

I have read that the 3BB was developed in the mid sixtys for NASCAR when they started to change the rules to single carb.

In the 60s the hi hp engines used 2x4BB to get the high cfm. The Hemi, Z-11 427/409 W engines, hi po Buick and Pontiac and even hi po Corvette 327 engines all used the two 4BB.

The 3BB used one large oval butterfly in the rear to get higher cfm.

In about 1969 when the Holley 850 cfm DP 4BB and larger 4BB came out, the 3BB went away.

pics of a Motion Phase III intake system, 427C intake, 3BB Holley and "fly eye" air filter

Google "Holley 3 barrel carb 950 cfm" and there is this thread here that may give you some insight... http://www.camaros.net/forums/showthread.php?t=93812

I collect Motion stuff and have another Holley found at a swap meet that some may find interesting.

It has what Motion sold as the "gear drive injector kit".

This was a collection of parts that converted a single pump, vac sec, Holley into a double pump, mech sec Holley. It would work on the 3BB or 4BB.
The kit had a larger acc pump, two long squirter nozzles, and two gears that replaced the vac sec linkage.

You drilled 2 holes into the air horn to run the long squirter nozzles into the secondaires.
The large volume acc pump would squirt all 4 barrels and the gears would mechanically open the secondaires.

I have talked to people who ran these and was told it worked but not all that well.
The gears would jam. Then you would go buy a new Holley 850 DP.

I collect Motion stuff and have another Holley found at a swap meet that some may find interesting.

It has what Motion sold as the "gear drive injector kit".

This was a collection of parts that converted a single pump, vac sec, Holley into a double pump, mech sec Holley. It would work on the 3BB or 4BB.
The kit had a larger acc pump, two long squirter nozzles, and two gears that replaced the vac sec linkage.

You drilled 2 holes into the air horn to run the long squirter nozzles into the secondaires.
The large volume acc pump would squirt all 4 barrels and the gears would mechanically open the secondaires.

I have talked to people who ran these and was told it worked but not all that well.
The gears would jam. Then you would go buy a new Holley 850 DP.

This was the Holley 3916 carb, lots of guys added this on as a single but like others said, the 2x4 carb was probably as good. Guys added the long squirters to try and make it more streetable. Sometimes on low rpm dump, the carb would just fall on its face but cammed right, you better hang on. Saw lots of these on BBC cars.

The Holley pictured with the "gear drive injector kit" is stamped
3878261-EH
list - 3310
date 923

If I remember right, it is a Chevy service counter 780 vac sec "Z-16" carb built in 1969.
The 3310 was originally used on the SS396 1965 Chevelle Z-16 and was a popular replacement carb with the hot rodders.

They were sold at the Chevy dealers for many years back in the day.

Someone added the "gear drive injector kit".