Wooly midrange on 115 Merc

[ahortstumpy2005]

Hi
I have a mid 80s vintage Mercury 115 oil injected. When i acquired it
only 3 of the 6 ports were receiving a spark. I rectified this with a
new switcher unit. But since then it has always had a problem if you
boot it so to speak. It refuses to rev under load (fine in neutral)
unless you very slowly go up the rev range - by slow I mean taking
several minutes from 1000 to 6000 revs. The carbs all seem ok. Is the
direct injection mix at fault - too much oil fouling the plugs? Can I overcome the
problem with hotter plugs? Or is it a fuel supply fault/excess oil in the mix. Any
suggestions greatly appreciated. cheers.