72 coupe-rebuilt 350 9.5/1 comp-ran great for one month then started losing power-edelbrock rpm heads, mild cam, manifold, timing chhain, and q-jet-crane roller rockers-msd 6A-all parts are new except stock distributor w/pertronix-just doesn't seem to be firing right-rattling in valve train when you really try to get on it-carb has been gone thru twice-could it be the vacuum advance???-plugs are fouling -black-which shouldn't be happening w/msd box-ive taken it back to the shop twice-he said run super in it-I said that's all I ever use-stumped-help????

If you really have rattling in valve train then a rocker stud may have come loose,rocker nut came loose,cam/lifter defective ,worn lobe/s/lifters,etc.

I would 1st warm up the motor and pull the plug wires off one at a time to find out which cyl/s are not firing. You can buy a special set of plyers made/insulated special for doing just this. Also hold each wire close to the block to see if a nice blue spark jumps out to ensure each wire is ok along with the Cap/Rotor too.

After you find the bad cyl/s(if any) take a comp test on those cyls and while your at it the rest of the motor too. Do this with the motor warmed up,the coil wire out or pwr to ign cut off and the throttle locked open to allow enough air into the motor. If you do not open the throttle you will get erronious comp readings.

You should see anywhere from approx 120-180+ per cyl compression depending on your pistons/heads/compression/cam/setup. The point here is to have a small deviation from cyl to cyl like approx 10% or less.

Now if a rocker is out of adj or you cam/lifter/s are bad then that will affect the compression reading/s too.

I would next remove the valve cover/s on the banks with the misfiring cyl/s and readjust the valves with it running. Use approx1/4-1/2 turn from zero lash for a hyd cam which i assume your running since you stated a mild cam was used but corret me if i am wrong on that. Also make sure to use the oil restrictor clips or al foil molded over the ends of your rockers to eliminate or at least greatly reduce the oil mess that adj the valves on a hot running motor with a hyd cam can create.

Clean or replace any fouled/dirty plugs too before you start the valve adj.

Also,watch to see if all the intake/exhuast valves are moving up/down the same approx amount. If any valves are moving less than the others of the same type (int/ex)then re-adjust. If any like type valves (int/ex) are still not moving the same amount up/down after the valve adj then the cam/lifter is bad for that cyl . This would mean you need a new cam/lifters at the least & maybe more depending on the damage at that point as a result of all the metal particles from the worn cam that got into the oiling system.

To be safe also check to see if your firing order is correct,18436572,rotor spins clockwise,1357 is on dr side,2468 is on pass side just in case this could be the problem.

If all checks out with your valve train,comression,and ignition then the black plugs could be caused by low intake manifold vacuum and the Q-Jets power poiston opening up too early causing an over rich mixture.

The lower intake maniflod vacuum can be caused by a few things,a vacuum leak,retarded timming, perf cam,etc.

But the 1st thing i would check would be your timing,most perf cams need at least 16-18 deg btdc intial timing not including your mech or vac advance so if it's not at 16-18 deg btdc crank it up.

Next after you get your intial timing adj then re-adjust your carbs idle mixture screws and idle speed. Then i would next hook a vac gauge to your full on intake vacuum to see what it idles at (auto trany in gear).

If your idle vacuum is approx 15-16 inches and above the older 60's-very early 70's Q-Jets will be ok,but if it's a newer Q-Jet like 72 ish and above your power piston spring could be to strong due to the lean smog motors with milder cams that produce more idle vacuum resulted in a leaner fuel calibration being implemented into the complete operating range of the carb. These leaner calibrated carbs will pop the power piston up at a higher vacuum than the older Q-Jets would due to a stronger spring and the lower intake vacuum signal that's caused by a perf cam,retartded timing,or an intake leak,etc.

Scott