timing problem

The factory springs won't give you full advance until to close to 4000 rpm. If you get the two spring MP kit and replace the heavy spring with one of the springs from the kit you will have all your timing in around 2500 rpm. Using both of the springs from the kit and you will have it all in around 1200 rpm.

The amount of initial timing is a function of the amount of overlap in your cam. More over lap requires more initial. Up to 20 degrees BTDC is not unusual with an aggressive cam. The way to find what the engine likes is to increase the timing in small increments while maintaining a constant rpm and adjust for max manifold vacuum.

On a stock distributor you may find that the engine wants that 15 degrees you have and that you will have more than the 35-36 total the engine wants. The quick way to check the amount of timing in the distributor is to glue a cheap protractor to an old rotor and tape a piece of wire to the housing as a pointer. Twist the rotor against the spring an measure the advance. Because the cam turns a 1/2 the speed of the crank you need to multiple the number you read by 2 to get crank degrees. If you have to much total you will need to restrict it by welding or epoxing the slots to limit the timing.