especially on a cold start
my last Merc was a 2003 90 2 stroke... and would be hard to start after sitting if I forgot to pump up the bulb
routine was. when starting up after sitting ( cold start ), to make sure I got the bulb pumped enough time so it was hard
then, using the key, prime it 5-6 times
after that. it started right up the rest of the day
man, that motor just kept getting sweeter and sweeter
...may be a place for you to start looking
Sometimes its too easy to overlook the obvious....