I have a new 350 chevy engine in a 84 chevy pickup. I HAVE A POP OUT OF EXHAUST WHEN I RAP ENGINE UP. WITH A TIMING LIGHT ON IT THE MARK ON THE BAL. WONT COME CLOSE TO TIMING POINTER. I DROPPED DIST. IN AND OUT ABOUT A DOZEN TIMES IT DOES NOT HELP.I EVEN INSTALLED A NEW TIMING SET IN THINKING THAT TIMING CHAIN WAS INSTALLED WRONG IT WASNT.TRUCK IDLES OK AND HAS GOOD POWER BUT AT BASE TIMING IT SHOWS ABOUT 50 DEGREES OR BETTER. TIMING MARK ON BALANCER IS BEHIND WATER PUMP.DO YOU THINK I HAVE A DIST. PROBLEM OR CAM ISSUES OR VALVES. WITH A VACUUM GAUGE HOOKED UP IT SHOWS AROUND 15 WITH SOME BOUNCE IN NEEDLE.

Generally after you install a reman. set the timing and break in the cam. Change the oil, pull the valve(check valve) covers and check the preload on the hydraulic lifters. This may be causing your low and unsteady gauge reading. As for your timing mark, with the #1 plug out bring your piston up to TDC using a tool that you wont lose in the hole. Check the mark on your balancer and If its not within 2-3 degrees from TDC than either the balancer is damaged or your on the wrong bank.

Yes, check that balancer mark against real TDC.
Are you disconnecting any vacuum advance during tests?
Did you check the plug wire order one last time?
Are you sure you are on the No. 1 plug wire?

You did not state if the pop is during acell or decell.

Popping in the exhaust during decel is caused by air and fuel burning.  If your engine has an air-pump, it could be discharging into the exhaust during decel, a guaranteed bang.

If it is a light popping and not a backfire, your fuel mixture is too rich and bleeding fuel during decel.  Also, if the exhaust manifold has a large crack or gasket leak, it could ignite a rich unburned mixture in the manifolds.

Popping during acell is typically caused by ignition failure, usually plugs or plug wires, or a VERY lean fuel mixture.

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