Did some further investigation, took the muffler off and piston is in pretty good condition, cleaned the carby as well just to be sure. The muffler outlet tube had a little carbon buildup so scraped that off. Put it all together, hooked up the compression gauge and again zero. Tried to fire it up and starts first time. Turned it off, tried again and started first time. Yes it's a turbo, this is the first time that my compression gauge has let me down.
