Rebuilt my MC2100 recently, (inlet needle seat was passing fuel) & installed a new fuel filter.
I am now experiencing a kind of intermittent problem at 55-65mph. Seemed like a fuel problem, percolating fuel or something.
With pedal holding a given speed, it would coast, then accelerate back to speed.
It was like a slowmo bucking.
I replaced the 7.5 power valve with the 8.5 one the Holley video procedure suggested. I thought it was cured, but it wasn't.
Today I retarded the timing from 8*btdc, back to 11*btdc. Seems to start easier, & run smoother. Acceleration is much better too. I'll see if it cured the stumble tomorrow!
Nothing else has been worked on with the engine since the carb rebuild.