[TomEV]

I'll second that jakobnev said - many conversions use a three-piece system which includes a vacuum pump (you already have this), a vacuum switch (about $40), and a vacuum reservoir (can be made from a length of 4" to 6" PVC pipe - cheap). The switch will turn on the pump when the vacuum becomes depleted while you are driving. As you found out, you need the vacuum booster right away when stopping, so a vac reservoir is needed.