Can anyone suggest jet sizes for a 509 with 420 Mega Blower and two 4150 carbs. I have 74 front and 82 rear with 4.5 powervalve. The engines run very rich at idle and foul plugs.

Jeff jetting will not really effect idling. Double check float levels and make sure your carbs are not dribbling or dripping anything inside at an idle. Double check your power valves to make sure they are good. Last but not least what kind of a vacuum are you running at idle. If your are at or below 4.5 your power valves could be opening. If it is rich at an idle the jets are not the problem.