I got a used holley marine 750 vacuum secondary, rebuilt it and just got it on the water today for the first time. around 3500 rpm, if I ease into the throttle, it will stumble and 1 time out of 4 it will have a small backfire before the rpms increase. So it seems like it is going lean as the secondarys are opening. I am going to try some other secondary springs, but should I also richen the primary jets a step or two? The bog I can handle with springs, but the lean backfire has me concerned about the overall a/f ratio on the primaries.