My previously well-behaved '77 Merc 700 has developed a bad habit on its last two outings....initial start up and acceleration to top speed is fine, but after dropping back to a slow crawl in no-wake zones, it tends to stall when I push the throttle forward. If I do it slowly, it'll eventually get up to full speed and run OK, but that's not gonna make my daughter happy on her skiis. Vent on fuel tank is open. Could this be fuel pump? Plugs? By the way, what are the right plugs for this engine...I just bought it this spring, and I'm not sure what's in it, or if they're the right things.