Nitrous on a 340 100 shot

What kit? Look at the instructions would be my first suggestion. There will be recommendations on fuel pressure and jet sizing.

Just a baseline to consider from running this stuff off and on for 40 years. If the fuel jet is larger than the nitrous jet, it's most likely a FAT tuneup. It can be cleaned up a lot.

An AFR meter helps a lot. Have the tune up on the engine great, then add juice. Tune juice to the same non juice max MPH AFR if running at the track. Runs best MPH at 12.2 on motor, run the juice at 12.2 as well.