Yamaha jults and cuts-out at full power ...HELP

[Haydondo]

I drive a 3.8m Humber RIB with an old 2-stroke auto lube 75 hp Yamaha engine on the back, starts idles like a normal 2-stroke but when going full power it Randomly jults and even cuts out at time then starts right back up and same again.
Any Ideas

 

[robert graham]

I'd look carefully for loose or corroded wires and electrical connections....including battery cables.