Causes of slow spark?

I"m guessing this is a BB Mopar of some kind
If you have an electrical issue Del can fix you right up.
In the meantime, here's how you set your timing.
Put the #1 piston at TDC compression. Then back the crank up to 10* Advance. Then back it up another estimated 5* for a total of 15*; Accuracy is not important.
Next , put the Vcan anywhere that you can rotate it 1 to 2 inches before it hits something, when you go to advance it. Pull the coilwire out of the D and near-ground it. Turn the Ignition key to run. DO NOT CRANK IT. Back under the hood, advance the D until you get a single spark. Back up and repeat. And a third time. Snug the clamp. Turn the key off. Pop the cap, and with a Sharpie mark the D on the outside as to where the rotor tip is. Put the cap back on. That Sharpie mark better be right under,or very nearly under, a tower. Whatever tower it's under is now to be designated ;Number one plugwire. Make it so, and rewire as necessary the rest of the wires.......in the correct firing order, and in the correct direction. Lock the D down. Your base timing is now set at a place that is guaranteed to fire the engine.....if the cam-timing is good.. You can set the timing by lite after you get it running.
Now, as to the electrical; Del will fix you up;
just make sure your pick-up is wired for the correct polarity, as to in which direction the reluctor vane passes by it. SBMs rotate opposite from BBs. If you reverse the polarity after the start timing is set as above, you will have to redo it
After you get it running, you will have to reset the power-timing.

May the Force be with you