[Vwdiesel] Decoking pistons

[mark shepherd]

Greetings,
Hopefully someone will be up on the other side of the world.

Just taken my pistons out for a rering, I was having a 'little difficulty starting. Fuel economy averaging about 45 to 48 UK mpg. 3 pistons have single stuck rings,top or middle some of the gaps could be as big as 1/16th- 1/8th of an inch!!
Bores good, and hastings rings fit to middle of VAG gap spec.  Pistons are great and so are all bearings. It loks like my nocking for the last 20 to 30 ooo miles was exhaust valve clash. I always set belt accurately, but I overskimmed the head, and so this mayexplain that.

However my question is this.
Should I remove the thin layer of carbon deposit between top ring and piston face? 

Regards
Mark