nos problem

An aftermarket ignition is a good thing to have when running a nitrous system, but no...it's not necessary. Do you still have the stock fuel pump? If so, that is your problem. Once you go up above a 100 shot, you should have a larger than stock fuel pump. The Hobbs switch on the nitrous system that monitors the fuel pressure, could be cutting off the flow of nitrous due to inadequate fuel pressure. Also, you should have a nitrous filter in your system. You might not be aware of it's location. Check out your instruction manual. The nitrous filter (which is just a screen) should be located inside one of the larger fittings that bolt onto the solenoids.