Is it solved yet?
Did any of these solutions work? I've been checking back waiting for a "thanks, that did the trick" because I too have my grandfather's circular saw and it does the same thing. It's solid metal casing, using the same blade that was on there when he died - HSS, not carbide tipped but still quite sharp. The only difference in the saw between when he used it last and when I try to use it is that it has sat in a metal box for 20 years. So if/when the correct answer is found, please post it here.
Insert witty signature line here.