[Eljaro]

I took my Contemporary out today after a mayor upgrade process which included a new TKO 600 gearbox, new waterpump ,a new differential cover, shimming the dif, and new yoko tires.
All very nice, especially the gearbox. Unfortunately all this did not help do do away with one simptoms which I can not resolve.
The engine stalls when breaking hard.
I have the jet extenders and special floats with the cutouts, the fuel level is set right just dripping out of the check hole, the vent pipes are in both bowls, the idle is set to 700 and the idle screws 2 turns out. I have raised the gas pedal so I can brake and when almost full stopped push with the foot sideways on the gas to keep the engine running.
There are no pops or backfires, so it seems to be a simple lack of gasoline. What can be done?