big block belches flame

First off thanks to everyone who replied to my last post. This is the same engine as in my previous post (400 big block chrysler, not sure what year). It has a non-stock cam (I don't know the specs, it was installed by
a previous owner and the guy I bought it from didn't know either), a non-stock electronic ignition (once again previous owner)with no vaccuum advance, and a non stock Holley 650 four barrel carb. The problem is that it seems like there is more vibration than there should be at idle in gear or in park, but it doesn't seem to be misfiring and the cylinder compression is normal. When I hit the throttle hard enough for the secondaries to open, it backfires and belches fire out of the carb, then proceeds to have no guts whatsoever. I ran some lucas fuel system cleaner through it and changed the oil and spark plugs, bought a Holley Trickit for the carb and rebuilt it because the secondary float needle was sticking and the secondaries are now operating normally and are getting fuel. I checked the compression in all cylinders and it was normal. The distributor cap and rotor are in good shape and I just set the air gap. I checked the timing and it was set at more than 30 degrees (!) before top dead center, so I advanced it to 7 1/2 degrees before top dead center, and it behaved the same only ran worse, like that was too much advance. It has fresh fuel in it also. Starting to run out of ideas. If anyone could steer me in the right direction, I would be grateful!
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Your total timing should be in the 36 to 38 range with a non vacuum set up. That means bring the rpm up till it advances no more mechanically and set it at 36 would be a good start. You divd not say if it was a DP holley or a vacuum secondary! I'll assume it's a Double pumper mechanical secondaries. I hope it is not a Vacuum someone has converted to pull the secondaries open manually. (carb number please) It sounds like a lean condition as the secondaries open. Could be the squinter and accelerator pump are not functioning on the back barrels of the carburetor. Front system may need attention to and condition could be exasperated by too small of jets in the carb! Dodegem
sackattack84 wrote:

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It is a vacuum secondary carburetor. The vacuum mechanism for the secondaries seems to work just fine, though, and I can see the butterflies open when I yank the throttle wide open(can't get too close, though, or I might not have hair or eyebrows anymore!). What about the lack of a vacuum advance on the distributor? Could the electronic ignition module possibly play a part in causing the problem? Thanks for the advice!
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Found the problem(s). The secondaries were not getting fuel; fixed that and the problem persisted. Adjusted the timing back to 38 degrees before top dead center, which smoothed the idle out enough for me to notice a misfire in the engine. Upon investigation, I discovered that two of the plug wires were switched. Switched them back and now it runs like a champ, although now I'm going to have to readjust the carb and timing since it's firing on all eight. Thanks for the advice!
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Good and your welcome! which spark plug wires were switched 5 7 ?
sackattack84 wrote:

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Yeah, I think so. The rear two plugs on the driver's side cylinder bank
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That's them 5 7! Real easy to mix up and they fire one after another 18436-57-2 Dodgem
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