The possible causes of your problem are many.
Sight unseen, this includes anything from a loose, corroded primary ignition wire, a failing ignition coil to a failing fuel pump or relay. With no background information as to condition and recent repairs or upgrades, narrowing the focus is difficult.
Setting all of this aside, my first
guess would be to examine the throttle position sensor. That part is susceptible to wear/corrosion and, if worn, it can lead to dead spots while accelerating - although the engine will not necessarily stop running. With the ignition switch on, do you hear twenty-one clicks as you move the throttle plate? Next, as unlikely as it may seem, is your ignition switch sloppy or worn? You typically have to examine this where the ignition wires connect and not necessarily where the key is inserted. I am unfamiliar with your ignition system as it interfaces with the djet. I assume the distributor includes a provision for the djet trigger contacts. Naturally, you might consider examining the same and associated wiring for condition and function. Whistling "could" obviously indicate a vacuum leak, but it might also be a somewhat normal noise with a closed throttle plate and an engine that is developing vacuum by rotating without running ( ≠ spark or fuel) .
https://e9coupe.com/tech/dljet/dljet.pdf
https://members.rennlist.com/pbanders/DJetParts.htm
