On my 400, I have the EGR blocked off. I have the dizzy hooked up to a vacuum port on the intake. I have a Holley 2 barrel 2300 500 cfm carb. There is a miss and exhaust backfire on the passenger side and the back 2 cylinders are getting more gas than the front 2. I have the timing set and the carb tuned to where the driver side doesn't backfire. Any help is appreciated. Thanks

 

No matter what you do a Holley 500 will not work right it will always be too rich. The Holley will 350 work great though.

 

500cfm is about the minimum size for a 400ci. If you still have the EGR plate under it it could be burned out internally letting exhaust gases into the intake.

 

The hot exhaust gases are a possibility. I was thinking maybe a bad valve or two. I'll check the EGR and tell any news. Thanks y'all.