Help me get my slant running right

Here's my problem. I havn't had it that long. 70 swinger-slant.

It drove ok home but I remember some small backfires.

I moved the timing around because it was hard to start but the found out it was the coil- replaced it. Timed it by ear and sounded responsive and solid.

Drove it and when under load got lots of small backfires and would not accelerate. Tried moving the timing many times and always the same.

It has a new distributor, plugs, wires, rebuilt carb.

It seems like the PO was trying real hard to get it to run better.

My conclusion is probably the timing chain is sloppy. Any thoughts? How can I test for this. I don't have a timing light right now. May borrow one soon. Thanks! :munky2: