Looking for fresh ideas: I have a 1987 Evinrude 150 XP (STXCUR) Crossflow with top two cylinders (1 and 2?) misbehaving. When I try to rev the motor by actuating the carburetor linkage for the top carb only the motor will rev until about 1/4 throttle (top carb only -- other two carbs at idle) then spit (sometimes) and die on top two cylinders above 1/4 throttle. The other two carbs (middle and bottom) will rev independently up to full throttle. Compression is same on all six cylinders (90 psi). When top carb is slowly actuated to the point where the top two cylinder die there is still an ignition spark -- rather my timing light says there is (I cannot locate my spark tester). With the motor running, when I open the throttle valve on the top carburetor I can see the primary then secondary jets working even after the top two cylinders quit working.
Things I have tried: swapped bottom carburetor with top carburetor, swapped #1 and #2 coils with #3 and #4 coils, swapped spark plugs, and cleaned recirculation fittings. Even though they appeared OK when viewed through the intake manifold with the carbs removed, I pulled the intake and checked the reed valves (leaf plates) -- they are OK.
Any ideas?
Things I have tried: swapped bottom carburetor with top carburetor, swapped #1 and #2 coils with #3 and #4 coils, swapped spark plugs, and cleaned recirculation fittings. Even though they appeared OK when viewed through the intake manifold with the carbs removed, I pulled the intake and checked the reed valves (leaf plates) -- they are OK.
Any ideas?