New primary control switch problems
Your old stack switch reacted strictly to heat. If the burner was producing heat within a certain period of time after the call for heat the stack switch allowed the burner to continue to run.  The job of these items is to make sure that the burner does not continue to blow unburnt fuel into the chamber without a fire present. The 8184, on the other hand works in conjunction with a cad cell (light sensor) to insure a fire is present in the chamber preventing unspent fuel from being blown into the chamber.  One of the characteristics of fuel oil burning under highly efficient conditions is that it produces a very bright yellow flame. Cad cell technology works particularly well with this type of light, it reacts to these light characteristics. Here is the rub.  If the 8184 does not see the kind of flame it wants to see within a much shorter period of time is will shut down the burner and go into lock-out mode, requiring a manual reset to restart the burner.  So if the burner is not burning as efficiently as it should it will not produce the color of light needed to cause the cad cell to react. A good bet is that your need a nozzle replacement.  Another possibility is the fuel pump.  Both of these items are critical to produce that fine fuel film that generates the highly efficient burn needed to cause the cad cell to react in the allowed time. The nozzle disperses the fuel into tiny droplets (we call it atomizing)into the chamber for burning. These nozzles become plugged with dirty fuel. They, as a consequence cannot produce the bright flame necessary to cause the cad cell to react. Additionally, the fuel pump could be the problem. As it ages it cannot produce the pressure necessary to atomize the fuel.  Additional factors are involved but hopefully this points you in the right direction.  A good tech can diagnose and repair this issue in a jiffy.  Good Luck.  PCL.