My original '70 (pictured at left in my avatar photo) was stock (Aisin) when I bought it in '78.
In my quest for better power and mpg I added an exhaust header and Holley 350 2bbl carb.
The improvement was dramatic, to say the least. I swapped both items at the same time,
so I can't say how well the Aisin would have performed with the new header. Mpg were very good.
I found the Holley to be easy to tune with jets and other parts readily available in the USA,
as was the knowledge base for the swap. The Holley 500 carb may be a bit much depending on your build.
My current 40 has a 2F and came with a Weber 38 2bbl. I find it to be much like the Holley in that tuning it is
very straightforward with the exhaust header my engine has. Jets, other parts and knowledge are easily found.
My opinion is that once you head down the performance path, as you are doing, changing the carb is no different
from changing the header or cam or distributor, etc. What matters is how well the components work together.
Many if not most of the people on this forum prefer original equipment but they may not be on the same path as you.
I'm glad my '63 40 has the 2F and a header. I could probably make the Aisin carb work if that was what I had but the
Weber works great for me and gets very good mpg as well. I like the fact that they are still making new ones, too.
Good luck with your project!
