Strange issue.
I have a 1992 XP 587 white with the following.
• Rebuilt Carbs (Mikuni Kits)
• New Solenoid
• New Rings (honed cylinders; 140 compression on both)
• New top end gasket kit
• New Exhaust gaskets
• New Battery
• Black Fuel lines (No Grey Tempo)
• Inline clear fuel filter...