A long shot, maybe the BFF Brains Trust can help.
JD STX38, black deck model, no model numbers (apart from the Kohler engine numbers) to be found, but there is a date on the underside of the seat which looks like Aug 9 1996. Google brought up numerous refs from Yankeeland, and reading them it seems there is a multitude of variations for the STX38.
Problem: mowing normally for about 10 mins., and the engine dies. Push in foot clutch (i.e. transmission clutch, one pedal only, right hand side) and switch off mower blades' electric clutch - engine starts & runs normally.
Foot clutch disengaged, engage electric clutch - engine dies.
Leave electric clutch off, leave foot clutch disengaged, engine starts, engage foot clutch - engine dies.
Engage park brake (which holds the foot clutch disengaged), engine starts, disengage park brake, engage foot clutch - engine dies.
Jumper seat safety switch and test above - no change.
My assumption from all above is that there is a safety switch on the park brake, and it is in series with the seat safety switch - i.e. if either one is open, engine dies.
Does that sound reasonable, and if so where is park brake switch? Not being funny here - it's not easy to see & feel much without turning the machine upside down!
The US sites suggest checking the chassis earth. Found it (not where it is supposed to!) and it is tight (didn't lay a spanner on it to check - would have to remove a back wheel to do that).
Found two different wiring diagrams, but with no serial number it is hard to decide which one to use first - apart from the problem of claimed numerous variations.
Tried an online tech, but for the cost of AUD59 I might as well take it to the local workshop.
Any thoughts anyone?