1982 26' Bayliner Explorer Volvo AQ125/270 outdrive- won't rev above 2900 rpm under load.Engine bogs down & sprays gas out of the carb while fouling sparkplugs of cyl. 2&3.Return the throttle to 2900 rpm & it runs fine. This engine starts & runs flawlessly up to 2900 rpm under load. It also revs...