motor runs like dog poop

A few days ago my motor started to run like pure dog crap out of nowhere. It is a 135 Optimax 2stroke In idle it fluctuates nearly 100rpm and when i increase the speed it still does the same thing. My first thought was an air issue, but I can't find anything wrong with the intake or any disconnected air lines. Also thought fuel, but a different motor runs fine on the same tank. Then I pulled and replaced the plugs, but still the same thing. Then I thought maybe I lost a cylinder. So I pulled the wire off of plug number six so it wouldnt fire and the motor sounds like it is running normally. Checked the plug on the other end and it was clean. Plugged it all back in and it is back to running like poo. What in the world would make a motor run better on 5 plugs than 6, especially since they are all brand new plugs. My guess now is a grounding issue somewhere but i cant find any missing grounds