You are confusing the C-75 to C-85 which indeed used a larger venturi and
Main jet. The A-65 to A-75 change was basically just a change in the red
line. No Carb changes. The Large end of the connecting rod had to be
drilled for a squirt hole and this was done on the later A-65 for longevity.
The RPM was boosted from 2300 to 2600 by using a flatter pitched prop. The
A-series Continental manual also recommends a slight timing change for the
upper plug to 29° and the lower to 32° The Carb venturi is the same 1.25
for both the A-65 and A-75


--
Cy Galley - Aeronca Aviators Club
Newsletter Editor & EAA TC
www.aeronca.org
Actively supporting Aeroncas every day


wrote in message
oups.com...
IIRC, the A75 had a slightly different carb venturi diameter and a
larger main jet in addition to the larger piston pin.

Dan