JD Z225 dies when brake disengaged?

My z225 dies when I disengage brake - handles out, blades disengaged, sitting on seat. It starts great, but as soon as I take off brake it dies. I've checked seat sensor and blew it out with canned air,checked fuses under seat. It starts great while I'm sitting - if I stand it dies. I've tried with transmission disengaged with no differance