[Caprimaniac]

25- 38 is very lean; agreed. Some say that the AFR reading while idle could be a faulty read because the exhaust gasses travel at such a low speed ++. So in reality they might be lower.
And on idle the AFR can be really high, not causing any trouble.

As far as I can remember....

Will still put a coin on idle screw adjustments.

You could do a test to see WHEN the plugs soots up: at idle (fresh cleaned plugs, warm engine) and on full throat/ accellerating (again fresh cleaned plugs, warm engine)- dont' forget to turn engine off (with clutch pedal in) in the midlle of the pull...