[Shaggy]

Sounds to me like a possible sticky solinoid. When was the last time you rebuilt them?

I have run alot of nitrous through the years and have run very few purge lines. I have always just "purged" during burnout by bumping the activation button real quick(if it is a 2 stage system then have 2 manual activation buttons on to activate each step seperatly to purge this way). if i am in a street car and spraying from a roll then i may get a littlte bog but then it picks right and goes. On a small shot (250 or less)some fuel ratio guages react fast enough to see the rich condition but but most bounce around enough not to really see it. on a hundred shot you aren't adding enough fuel for you motor to lay over on itself for the instant that it takes for the nitrous to get through the line/solinoid/jet.