Barry martin

This is my first post, please be patient with a 61 year old rookie, bought this bike about a year ago ran like scalded cat for about 2 miles then died. After my feeble attempt at trouble shooting, took to repair shop $700.00 later got bike back home, ran like scalded cat for about 4 miles And died again. Will not start, very week and intermittent spark about 20% of the time. Any advice?