I had an issue with my 750 DP. I have to use a 6.5 power valve, because my idle vacuum in gear is only about 8.5. (rule of thumb 2 numbers below idle vacuum) If I give the car say half throttle I will get a short lean spike, because the vacuum does not drop enough to open the power valve. Not a problem if I give more throttle and the vacuum drops below 6.5. I went up one primary jet size and the lean spike is not too bad. I run an AFR around 12.5 to 13 at cruise which seems to be as lean as I can go without worsening the part throttle issue. By the way, my secondary does not have a power valve.
