i have an 87 bayliner with the 4 cyl volvo penta aq125 a in it and it just wont start , and the thing i dont understand is that its getting everything an engine needs to start, its getting a nice blue spark and plenty of fuel and it still just wont start. ive done the plugs,cables,points,cond.,cap,coil,button,even had the carb rebuilt and it still just will not start.it gives a lil backfire out the exaust so we know its firing.what could we be overlooking or just plain ol doin wrong. thanks