▁States ▁Coast ▁Guard ▁in ▁ 1 9 9 9 ▁( see ▁fall , ▁ 1 9 9 9 ▁B S AC ▁Min utes ), ▁agree ing ▁to ▁limit ▁the ▁speed ▁of ▁a ▁P W C ▁to ▁ 6 5   m ph ▁in ▁a ▁specified ▁test ▁protocol . ▁ ▁Before ▁ 1 9 9 1 , ▁P W C ▁em issions ▁were ▁un reg ulated ▁in ▁the ▁United ▁States . ▁Many ▁were ▁power ed ▁by ▁two - stroke ▁cycle ▁engines , ▁which ▁are ▁smaller ▁and ▁l ighter ▁than ▁four - stroke ▁cycle ▁engines ▁but ▁more ▁poll uting . ▁Simple ▁two - stroke ▁engines ▁are ▁lub ric ated ▁on ▁a ▁" total ▁loss " ▁method , ▁mixing ▁lub ric ating ▁oil ▁with ▁their ▁fuel ; ▁they ▁are ▁estimated ▁to ▁create ▁exhaust ▁in ▁excess ▁of ▁ 2 5 % ▁of ▁their ▁fuel ▁and ▁oil ▁un burn ed ▁in ▁addition ▁to ▁the ▁products ▁of ▁incomplete ▁and ▁complete ▁comb ust ion . ▁ ▁The ▁ 1 9 9 0 ▁am end ments ▁to ▁the ▁C lean ▁Air ▁Act ▁allowed ▁the ▁U . S . ▁Environment al ▁Prote ction ▁Agency ▁to ▁begin ▁reg ulating ▁all ▁recre ational ▁marine ▁engines ▁including ▁P W C , ▁as ▁well ▁as ▁other ▁off - road ▁internal ▁comb ust ion ▁engines . ▁The ▁ag ency ▁began ▁a ▁dialog ue ▁with ▁manufact ur ers ▁in ▁ 1 9 9 1 , ▁resulting ▁in ▁reg ulations ▁that ▁were ▁en act ed ▁in ▁ 1 9 9 6 . ▁These ▁reg ulations , ▁set ▁to ▁phase