Smoke!

[davidwheeler]

Aprilia with recently rebuilt engine started to smoke excessively though still going very well.  I put her away fearing a broken ring or worse and only looked yesterday.  Took a spin rund the block and then started to read the plugs.  No 4 was loose - about two turns, just about half way out!   Put in a new plug and screwed it in tight and went round the block again to burn off the oil - perfection.   In an ordinary engine a plug that loose would be obvious but sitting in the oil bath seems to have been enough to maintain enough compression to allow it to work despite the insulator being black.   We live and learn...