What is inside the exhaust pipe?

[Texasdoc]

Don't know if it means anything but I found that my timing pointer was 4 degrees off today. Checked with a piston stop and found the 4 degree discrepancy. I have noticed a decrease in power lately and some misses at high to WOT.

Today I took off my vacuum advance to see if I was over-advancing at high throttle (not WOT) causing detonation/missing. This made the miss worse, even causing a backfire thru the exhaust.

When building the engine I had way too much slack in the timing chain so I had to get a shorter chain (don't remember how much shorter but Clovis made a double roller that was shorter). To get the cam with the shorter timing chain within specs while using the degree wheel, I had to install the cam 8 degrees advanced instead of straight up. I can't do the math in my head, but would the advanced cam combined with the retarded timing cause the miss and/or squeal? I was actually only running about 32 degrees total - all in at 2500 rpm.

I think that when I had the vacuum advance attached, it was advancing a little at heavy throttle "protecting" the engine from too little timing. Without the vacuum advance, it was too retarded and started backfiring. I set the timing mark to 41 degrees (41-4=37 actual degrees total). I didn't get to test it before having to come to work.

Any thoughts on if this could be the cause of any of my problems?