Engine Ignition Spikes

OK Gang,
here's a brain teaser for the engine gurus. I have a 1986 Jeep CJ-7 with a pre 1975 Chevy 350. I have a moderate cam (unsure as to lobe) I installed an MSD 6A ignition module and I was running Accell 8 mm wires. Everything was cool and the engine ran like a top. Lot's of good accelration in for a Jeep. I just recently installed MSD 8.5 mm wires and I installed a brand new dual exhaust system with Block Hugger headers, and 2" dual exhausts with flowmaster 40s. Here's the problem: The engine now spikes 150-200 rpm about every 10 seconds. The spike only lasts for a fraction of a second, but you can see the spike on the tach and feel it in the engine. Also, when I was driving up the hill in fourth gear, every time the ignition spiked, the engine knocks. Also, the engine doesn't seem to be as powerful as it once was. Looking for any insight you may have. Thanks.

Check your advance mechanism; possible broken spring, binding pivot, weak spring, vacuum leak (if vac adv), bind in vacuum arm, loose plate under weights.

what was the exhaust before? you now have a hi-flow, have you leaned it out too much?

put the old plug wires back and see if the prob goes away - at least you can determine if it is plug wires or exhaust.

when doing the work, do you knock anything loose (vac line, wire, etc?)

check plugs and wires - all ends on tight, no arcing, etc? no cracked plugs? dist cap OK? wires seated in it OK?