472 hemi misfire

[wcw]

here's what I have, just got a 70 cuda with a 472 hemi auto tranny it starts good runs good idles good burns the tires good until i hit wot then it backfires and runs terrible until I let off runs good right through 3/4 throttle it has a 4150 holley vacum secondaries jets are 80 front 82 back 5.0 pv 7hg vacum at idle, less then 300 miles on the motor 14* timing 28 total I have changed: motor wiring harness, coil, voltage regulator, battery cables I tried all the secondary spings except the very lightest timing started at 11* went to 18* 30 total not good so settled at 14* not sure where to look next hope someone can help
Thanks Bill

 

[moparleo]

How about a picture of the set up ? Did it run this way for the last owner ? What manifold ? Single 4 BBL ? Idles good ? 7 hg at idle ? Sounds very low. Vacuum advance distributor ? Vacuum hooked up ? Only 30 Degrees total advance including initial advance ?

 

[wcw]

The last owner installed the hemi and drove it about 75 miles said it scared him so he parked it for about 9 years ( he was 75 at the time) said he started it every couple of weeks to hear it run. this is a mopar crate motor so i think it is a mopar manifold single 4, 850 CFM idles great also has a 3600 stall. vacum distributor and vacum is hooked up I sprayed cleanr around the base no indication of a leak there, idles at5-6 hg in gear, 30* degrees is when I move the throttle and the timing mark stops moving easy on the hard questions I'm a builder not a mechanic so alot of things I don't understand but I love it another thing on damp roads at 50 mph if you stomp it it will break the tires loose just before it starts popping. Sending photos as soon as I figure out how.