[Mesorah] the reversing vav

[Sholom Simon via Mesorah]

Dear Chevra (with a cc to two friends with whom I 
was discussing this yesterday after mincha)

I noticed that the two verbs at the end of the 
first pasuk and the first word of the next pasuk 
(of Ki Savo) were the "reversing vav" types -- 
changing the verbs from past to future (virishta, 
v'yashavta, and v'lakachta), but that only two of 
them had the accent on the last syllable.

I was then trying to remember the reversing vav 
rule and it's exception.  My best recollection was:

this rule (that the accent must be on the last 
syllable) only applies to “perfect” (past) form, 
not imperfect (future) form.  Further, it only 
applies to “regular” roots – not roots of ???, 
e.g., v’hanisi (you don’t put stress on the last 
syllable) – but that rule also has an exception, 
viz., unless the word comes before a word with a 
guttural in which case you do switch the stress to the last syllable.

I guess I am unclear which roots are exceptions 
to this rule.  Apparently Y-SH-V is.  But, as you 
can see, in the above sentence, I put ??? where my recollections failed.

Can anyone explain this  better?

Thanks!

Shavua Tov -- and KvCT!

-- Sholom