I had a similar problem on a motorcycle sidecar outfit. After dismantling the carburettors and fuel system and cleaning them multiple times I discovered it was a bad connection to the ECU. In a rather brutal manner I resolved it by reaching down unplugging and replugging the ECU connector after it cut out at about 100KPH. After that it never dared to do it again. I probably frightened the hell out of it.

Peter

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