I have a '78 boat w/ a 91 gm 350 4bbl carb & Volvo Penta OD. The boat is 24' IMP deep V. It has replaced dist cap, button, points, wires, plugs. Took the boat out and was doing fine for first 20 minutes. We were at a plane w/ throttle all open, when it started making pinging noise and spitting...