Type of breaker points

Guys, it's happening at 25 mph, long after the squirter is empty. And once through this and at a higher throttle setting it's okay again.
Heres my 2 cents;
At a light throttle setting, you will be running on the T-ports and idle circuits, all the way to perhaps 70 MPH.
At 5/8 to full throttle, she will be on the mains.
At moderate throttle, from about 3/8 throttle to 5/8,and under load, she will want to pull through the power valve system. See the connection?...........I think you're power valve system is on vacation.
But it seems not lean enough to cause a missfire or backfire, so then look for an intermittent exhaust restriction, perhaps a loose baffle in the muffler.
I suppose that if at this 25 mph is right on a transmission shift, sometimes the shift overlap pulls the engine down, requiring more pedal.
Happy hunting