'89 Searay 180 with V135 s/n c166937. Max RPM is 3500 and will intermittently jump up to 5600 at WOT while cutting in and out. I?ve eliminated stator, switch boxes and coils as possible cause and trigger checks good. Also replaced fuel pump, filter & lines and cleaned carburetors and installed new gaskets/needles & seats. Good spark on all cylinders. Looking for hints on what non-typical failure might be causing this problem. Thanks in advance.