I would not completely toss the idea of an elecrtrical problem...my 200 was surging exactly as you describe...we put a new power pack on and cleared it up completely...if a fuel issue is not apparent, take a close look at the Power pack...
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'74 V-20/ BF 150
'95 V-21/ BF 150
'84 V-20/ 200 2.4 Merc
'87 V-20/'18 F150 Yamaha
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