I'm hoping this group might be able to lend a little help. I'm in the process of trying to revive a SBC 350 in an old '59 GMC 1/2-ton. The motor is from a '72 A-body with a Quadrajet carb and an HEI distributor. It had been running reasonably well until about a year ago when the carb started flooding and pouring gas all over the intake manifold. I tore it apart for a quick clean and rebuild but thereafter its been a struggle to get it to start or idle at all. I've tried swapping carbs with a known working Q-jet unit with no change. I pulled the intake manifold figuring maybe something had fallen in and been sucked down one of the runners during the time I was rebuilding the carb and was restricting airflow to one or more cylinders, but it was clear. I've double-checked timing and it is at 16* at idle with the vacuum disconnected coming up to 32* by 2500 RPM. I've replaced spark plugs and wires, but not the cap, rotor, coil, or HEI module as all are relatively new and at least for the cap and rotor show virtually no signs or wear at all. I ran a compression test on all cylinders: 1 - 178 2 - 178 3 - 187 4 - 165 5 - 190 6 - 165 7 - 172 8 - 170 It seemed a little odd to me that 3 and 5 were so significantly higher than the rest, but not enough that I figured it would cause the engine to run this poorly. The thing that really left me scratching my head was the cylinder power balance test. As I was pulling spark plug wires and recording the RPM dips, when I got to cylinder 5, not only did the RPMs not go down, they shot up from around 620 to nearly 950 and stayed there idling smoother although not smooth. Once I reconnected the plug lead, the RPMs dropped back to 620 and really rough. I had a similar result with cylinder 4. All others recorded about a 50 RPM drop. I'm really not sure what to make of it. Any thoughts or suggestions would be welcome.