Check all wiring, my old D14 did that,
Mice had built a nest behind one of the side panels, they had chewed the covering off one ignition wire. As I was driving along, tractor moving over the plowed ground, this bare spot on the wire would swing against the steering column. Temporary cutting off the motor.
I am not that great of a trouble shooter, so it took me a while to find the problem.
I was about to tear into the carb, fuel tank, lines, wiring harness, etc.
Cleaned out the nest, wrapped the bare spot on the wire with electrical tape, problem solved.
Hope yours is as easy, but I felt like a fool after finding the problem.
Those little bastards can cause lots of problems.