Jim
I’ve been toying with a 7042240 Buick casting on the street. It was a circle track carb at one time and it does not have booster rings or primary needles. I bought a 5 gallon plastic pail that had three 7042240 carbs. Two were untouched and one with the mods mentioned above.
The ring / bulge remains in the main casting. It has been stated many times that such modifications on a street car are a waist of time. I would agree, however I am having fun learning how the different circuits impact or work with others.
I’ve been through both Cliff’s book and Doug Roe’s books, but they do not replace real life experiences.
Anyway, viewing your picture, the main air jets “appear” to be in that .050 - .070 range. IMO, too large for a carb without booster rings let alone the bulge removed from the casting. I have worked my way down to a main air jet of .030 with a 71 jet. I run AFR’s of about 14.4 – 14.7 at around 60-65 MPH. With the secondary disconnected, full throttled run is roughly 12.4 all the way to about 5k RPM.
What’s my point? In my case, reducing the main air jet size allows more fuel to pass through the main jet. In addition, higher differential pressure created by the use of smaller main air bleeds allows the main circuit to start flowing earlier. With your carb, I would first determine the size of the main air bleed. If you are in the .050 -.070 range, leaving all else the same, I would decrease the size of the main air bleeds and watch your plugs and AFR’s.
Now, anything mentioned above is a waist of time if you are running out of fuel?
Good luck
Cat
