Chappy, first of all, install a 6.5 power valve. #73 jets should be good but obviously aren’t. Are these the same jets you used prior to changing the exhaust, if they are, go up to size 76 for a day and then try 78s and in each case, check your plugs to see what color they are changing to. I imagine their current color is white or light tan. Tan is the color you want.