July 2009
The 400 2bl was a stock production item. The 2bl was a 500 cfm item and if it had been replaced 
since it came from the factory (to correct a carb hesitation problem) there will be two (2)
 additional accelerator drillings at the top of the horn of the carb throat. They are not small
 needle size like the factory ones down in the lower body of the throat but are about the size
 of a match stick diameter (about 3/32") diameter. You can check by having someone press down 
on the accelerator while you look down the carburator. You should see two large streams exit near
 the top & go into the carb throat. Also if you are using a light, you should also be able to see
 the two small factory accelerator streams coming out of the needles in the lower part of the bore. 
 This was a repair for the Rochester carb in the early 70's. At 70 MPH, stepping on the accelerator
 will convince most small block fans that you are running a 4-barrel. 

Also, the 400 should be a 4 bolt main block.  I own a 1972 RQB 1834 and this is its set up. I have 
owned several non-Avanti small blocks with this carb modification.  It is great!  The 400 2bl 4
 spd (in 4th) [3.93:1 diff] will set you back in the seat by depressing the accelerator at 80 MPH.
 Stock factory set up.

If you have the 400 2bl, before you change to FI, have some fun, make sure your carb has the factory 
modification [all my info researched in the early 1980's showed it to be a Rochester factory 
modification to cure the problem], put a kit in the carb, set the timing to specs, and go check it out!

Del Compton
1972 RQB 1834 [400/4spd]
1984 RQB 3851