Had the same Problem. Try squirting a little bit of water on the throttle plate shafts from the outside. It will stop the whistling if thats where its coming from. As a temporary fix I put a dab of wheel bearing grease on the outside of the carb where the shaft is. Eventually replaced the carb.
Some other good scams from the past: Tornado intake insert, STP, and my favorite the "magnet on the fuel line". It was suppose to line up the fuel molecules, LOL.
I will be on a road course later this summer. I plan on spraying 100 on the main straight to try and keep up with my kid's turbo Caliber. I have made hundreds of 1/4 mile passes with it and haven't had any problems.
I have been useing the Holly 110 mechanical fuel pump for years. 100 HP spray on a Magnum 360, 5/16 pickup with no problems. Runs high 12's, never goes lean.
After doing all of those things mine is still not reliable. My solution was to put in a speedometer with a trip odometer. I fill the tank and reset the odometer every time. I have an extra 120 MPH speedometer with the trip odometer if you want it.
The purge is used to get the liquid nitrous right up to the solenoid. The liquid causes the cooling (like A/C) when it changes state to a gas. The heat in the engine bay will cause the the nitrous to turn back into a gas after a while, so you need to purge out the gas right before each pass...