Ms 651/661 difference

[floriceeel]

Hi guys. Can someone tell me what is the real difference between the 651 and the 661 Stihl saws? The engine seems to be the same, 91cc. Maybe some carb or ignition difference, what do you guys know? I can't find any ipl to compare the part numbers. Thanks!

 

[huskihl]

I believe the 651 has a thicker base gasket to lower the compression for 3rd world countries with ****** fuel

 

[floriceeel]

Interesting. That could be verified by checking the part number of the gasket.