I would then assume plugs {at the proper gap and number}, filters were done. Battery is of sufficient size {1000MCA} and in good shape. If so, check linkage set-up, and be sure the TPS "sweep" is linear and consistent from idle-to-WOT and then back again. You'll need to have this done on the CDS at your Merc Dealer. I would also assume your fuel lines and primer bulb have been updated to the newest alcohol resistant stuff.....if not......it's time to do it all.