I'm a novice tuner who is hitting a wall, running out of ideas, and kindly need some help. I tune my Q-Jet by "giving it what it asks for" at the track as opposed to dyno tuning. It's a mild 4000lb car that runs 12.9/105mph. Steady idle of 14Hg in Drive and no vacuum leaks that I can observe. Total timing is 36 degrees.....16 initial/20 mechanical. Best ET and MPH is always with 78 jets and DG secondary rods on a "G" Hanger. Even richer rods like CCs slow it down and richer in the middle AX's also slow it down. Carb is factory 800cfm unit with only a 1/4" base gasket...no spacer. Float level is 1/4" and needle & seat is .135. I use a RobbMc mechanical pump with functioning return line. If I take fuel out and use 76s or 75s, ET and MPH suffers. If I put 78s back in, all is well. Choke pull-off release time is one second. Engine is 455 Pontiac with mild hydraulic roller 224/230 .552/.528 112 lobe separation. Rest of drivetrain is TH400 with 3:08. Stock cast iron intake but oversized cast iron exhaust manifolds and "X" pipe. I tune for "cooler" weather, which is what I prefer to run in. DAs around 600 feet to 700 feet is what the car likes. It seems to just want more and more primary jet but I'm having a real difficult time thinking even larger primary jets than 78s are needed to go faster/quicker. I'm starting to run out of larger jet options. Should I slowly add more timing? Have I plateaued with my set-up? Thank you.