need help with a Holley carb

I thought I would put this in the right forum. I have stated several times while on FABO that I am no Holley guy. Me personally, I wouldn't have one on my car if it was given to me. That doesn't made me a bad person because I have had better results with Edelbrock, This goes back to 2002 right after I put the Duster together. I had a 650 double pumper on it. I had a stroke in 2001 and wasn't getting around very well. I was going to the dr. office that day and I was going to drive the Duster. Started it up and it coughed. Burnt the top of the engine bad. Had to replace the intake, dist., wiring and hood before I managed to get it out. So that is why I don't like a Holley. bad time. Now I have this 67 GTO sitting in the garage with the same problem. Holley poured fuel and caught the engine bay on fire.
Spent last week doing the wiring, installing ignition module, dist. cap, hot tanking intake, detailing top of engine etc. etc. etc. Had the carb rebuilt by reputable guy from a machine shop who races his own dragsters and such. Put it all back together. Started right up, sounds good at idle and even sounds good if you bring the RPM's up slowly but if you rap on it from an idle, it has a dead spot in it. same thing my Duster did before it coughed. when you run the car for awhile and let it idle down and then shut it off, the engine wants to keep running some and it seems like there is a mist of fuel coming out the top of the carb when this is happening. I don't know very much about a Holley. On another thread I mentioned this problem so I brought it over here.
One member said it was called " run on ". said he thought it may be throttle blades open too wide at idle. maybe need need to set floats. One said to check timing.
This is what I have. Engine is a 455/467 CID putting out 515 HP. Motor was built by Butler Performance in 2012. everything was new in engine. carb is a 4781C Holley Chromate 850 CFM double pumper. Has Edelbrock D port 87 CC heads. Has an Edelbrock Performer RPM dual plane intake. It has a M6907 Carter fuel pump. I don't know if the guage on it is correct but it showed 8 PSI of fuel pressure on it when it was running. Timing is set at 36* according to the timing marks. That is also what Butler set it at when built. car ran great until the fire.
Would this be some simple adjustment on the carb causing this or do you think it would be something he missed when he rebuilt it. Do you think someone who hates a Holley could do this LOL. I put a call in to the guy who built it and was going to see if he could come over and adjust it. What do you Holley guys think. Thanks, Bill

Oh, I also put an Edelbrock # 9266 heat insulator gasket on it instead of the thin one that came with the kit.