I'm pretty sure it may have to do with the fuel mixture, its the best lead I have so far. Is that something designed to be commonly adjusted at set service intervals? The car does give off an unburnt fuel smell at times, usually noticeable at slower in town cruise speeds.

Or am I taking this the complete wrong way? I think the best way would be to replace the speedometer sensor on the trans and get that speedo working again and start calculating!

Edit, Also, how does the lambda circuit affect the engines fuel mixture on this engine?