If you can convert your Iswara's (I'm driving my brother's
car now) hopeless, problematic (wax auto choke !) Aisan
carburettor to your Nissan Vannette's carb, which I believe
is a far more reliable Hitachi, by all means go ahead.

In the first place, your electric choke is far more reliable
than the stupid wax-operated (very expensive too, costs
more than $400 if you order it, I am told) choke on the Aisan.

Electric (bimetallic strip) chokes hardly ever fail, and if they
do, it's a simple matter of disconnecting its linkage to the
flap on your carb and not using it. I used to drive an Opel
Gemini from 1983 to 1993, and the Nikki carb's electric
choke never gave any trouble. Nikki is a subsidiary of Hitachi.

Secondly, Hitachi carburettors are usually far more economical
and reliable than Aisans.

My last car was a Toyota Corolla KE70, and its Aisan carb,
even when I replaced with a new one, gave endless problems,
not to mention a gas guzzler.

This mechanic I know said he used to convert the Aisan on
this type of car to a Datsun 120Y or Nissan Sunny's Hitachi
for his customers, with far better economy and reliabilty,
at the expense of a slight loss in performance.

The secondary venturi typically opens at 3,000 to 4,000 rpm.