i haven't messed with one of those carbs in 50yrs but I do remember not getting it to work properly. I lot of that was lack of knowledge when I was 22yrs old. this is off topic but I remember having real fuel control issues with those fixed needle and seats. I think they are something like .075" seats and they didn't like pressure. if you keep in mind that those engines came with 3-5psi fuel pumps and most of those pumps wouldn't do 5psi you can see were a problem could arise with a 6-8psi pump which is what I used back in the day. I don't know if there's a way to get creative here but I doubt that .075" seat can provide enough volume without overpowering it with pressure. the carb i played with had a small brass balance tube between the primary and secondary bowls. that brass tube may be necessary for the fixed needle and seats but might become an issue if you do get creative with different needle and seats.