340 with Thermoquad and MSD distr. with 6A box, recent plugs, good wires. In my last Thermoquad thread I was diagnosing fuel leaking into the intake. Turned out to be a leaky brass float which I got fixed. This was a #6518s that I had rebuilt not long ago. ('74 440 "Industrial".) Also I had this really dialed in for my 340, great A/F #'s, good plug readings, etc. Call me crazy, but I looked at my parts carbs and see I also had a #6322 core ('73 Truck 440) in decent shape, so I decided to build up a backup carb. So I set it up with a new kit, similar jetting/rods, same settings, etc. The only problem with it was worn at the primary shaft, so I ordered one of those cool reaming tools with brass bushings from Carb Junkys on eBay. (That thing is so slick, and the process was easy and it now feels like a new carb.) So I decided to stick it on to test it. Started up, warmed it a bit, and went for a drive. Like the other one, I was getting 13.5 with light throttle, mid 14's at steady cruise, 15 or so on a bit of hill. All good, great TQ throttle response, etc. I get out of town, and with the very first WOT in 2nd, all of a sudden it craps out, starts missing badly, will hardly run, after a bit it started running a little better and I made it home. But on the return trip my A/F was now reading 10:1 and power was down. I pull the plugs and all are heavily black and sooty. Any ideas what happened???? With it being the first run on the carb I suspected it, but don't know how it could cause the motor to instantly crap out and be missing like that. But it doesn't seem like ignition would all of a sudden drop the A/F down to 10's. Thoughts???