Future ref is 2oz's for every 5 gallons of gas.Too much lowers the octane and too little won't cover the job.Two things you haven't said yet is if it has a in-line gas filter and if you have checked the fuel pressure.Just to have gas in the carb without know if you are getting the proper fuel pressure "can" cause issues.Have you sample read the plugs.......they can tell you a story about it that even while it was starting right you didn't know.( sample reading is a nice way of saying you should look at all of them)Did you say what color the spark is??.