I just replaced an fmf with a Kenny Robert’s exhaust on my 85 and it was a huge improvement everywhere in the power. Now it has a noticeable “hit” almost as soon as I get past 1/8 throttle. You can hear it and feel it hit and it just spins the tires or stands up and the power stays there until I shift and doesn’t fade out. My engine setup is basically identical to yours but I have CR ignition.I have a 38mm carb, cleaned up ports, 200 psi compression, running 110 octane, v force reeds and DRW ignition. Power with fmf fatty hits hard at upper rpm and very narrow power band almost nothing below 5,000 rpm. Switched to another unknown pipe I have and it tamed the hard it, gave more bottom but overall seemed to be slower but more manageable out of corners.