Hello, I've run into that problem many times also. You can check slop in the chain by taking off the dist cap and mark where the rotor is pointing, then rotate the engine by hand one way (clockwise or counter-clockwise) doesn't matter. Watch how many degrees the marks on the balancer move in relationship to the timing mark. Now move the balancer the other direction, as soon as the rotor moves see how many degrees the balancer moved in the other direction. Now, subtract the difference. If it is more than 6 or 8 degrees, the chain is bad. I've had them so loose that they wore a hole in the timing cover causing a leak!
Hope this helps, Jeff