I've been tuning my Holley 4777. I'm running quick fuel metering blocks. I've the Idle feed restrictors dialed in and it runs best with 40IFR's. All was good untill I put my new flowmasters on and now I have a miss at highway cruise speed (65mph @ 3100RPM) I can speed up a little and it will go away, if I back down it misses all the way to about 1500rpm. Do you think its jetting (71 prime 81 sec), timing, or need to increase the IFR's again. Like I said this started after the new mufflers.
PLUG WIRE.... You have a plug wire arcing out somewhere at highway speeds... Get some ISOPROPHYL Alcohol, mix it 60% to 40% water and put it in a squirt bottle, set it for MIST, start the car set the idle around 1,500 rpm, and slowly spray around the plug wires from cap to plug and watch for Green and or Blue Fire... There's your bad wire causing your on the road Miss.