I think your problem is that the 600cfm carb is to big for your aplication.

The Racing beats website recomends 465 CFM for a stock or streat ported 12a.

Some times bigger in not better esp. when dealing with carbs.

I used to race a RX3 about 15 years ago and am a good freind of Mike Lowe who owns Lowe Proformance and the 1979 turbo RX7 that has run an 8.33 at 165 MPH with out NOS.:o

I have heard him say this on many occasions.

I know the 465 CFM carb is more $$$ and hard to find but it will make your car much faster.

Eddie