That can be a dull chain, but its more likely an oiling problem which also can be a rail groove issue. Also, it can be that you have your chain too tight..
Yes, all of the above:
my bar started smoking (it was still cutting and throwing chips)
I stopped the saw here is what I observed:
- chain had tightened up due to bar groove filled with chips to the extent chain was being pushed out of the groove
- chain was under oiled, bar oil port was plugged with chips.
lesson learnt due not use a low profile chain with the L-shaped type rakers (stock 6401 chain is all I had at the time) if you have the bar buried on a high HP (681) saw that can hit the limiter in the cut with full pressure on a new sharp chain.
My guess is the the L-shaped raker impedes chip clearance at high cutting speeds and feed rates
I find I get the best chip clearance running a longer bar (32") with skip chain, much easier cutting than the throw away 20" bar and chain combo's that come with many stock saws