Your likely using the wrong Glowplugs !!!! your using OS plugs right ? or have threaded an OS into the button at some time ?

I really wish I could help you with your motor, but without me being there its very difficult to tell you what is going wrong....... I have seen several people have tuning issues with Picco's, but there was always an underlying reason.....whether it was user error or some unforseen mechanical problem....... But no matter what the cause there has never been a Picco I could not get running nice....

Most common issues i see are

1. Not using Picco plugs, far too many people using OS and Nova plugs, these plugs do not seat correctly and can cause leaks and odd tuning conditions

2. People moving the needles too far when adjusting... Picco's require far less needle movement then a motor like a Mach or LRP...in most cases I tune a Picco with slight nudges of the needles, 1 hour increments is too much..... All it takes is enough movement to feel the o-ring move.... If a person attempts to tune a Picco with LRP or Mach sized needle changes they will never be able to tune the motor

3. Trying to tune a Picco before the motor and chassis is fully heat saturated... Picco's will run extremely rich for the first 3/4 of a tank till it fully warms up, once it gets the proper heat into it the motor will naturally lean itself out.... Many people will tune the Picco while its still cold then find it leans itself out by the end of the tank.... You will not likely be able to warm a Picco up properly by idling, they usually need to be driven on the ground for a bit before they will warm up. Usually they will be amazingly rich on first startup , but once you start running them hard they will clear up and start running extremely crisp without even touching the needles.......... Far too many people will tune em in on the starter box only to find the motor leans itself out by the end of the tank....... Picco's need to be warm !!!!