32/36 Weber carb MGB dies when accelerating but when the progressive second butterfly throttle valve opens it revs fine at high rpm

i have a 1977 MGB with a 2 barrel progressive throttle 32/36 Weber carb. it will idle, but if i try moving at low rpm, the engine will jolt on and off. like if i was pressing the gas but rapidly switching on and off the ignition. my ignition seems to be fine, i tried new plugs. and the whole car ran fine just the day before.

heres the thing, if i go under the hood and bypass the first butterfly valve (which opens first out of the 2 in the progressive system) and open the high speed valve by hand, the engine revs fine. does this sound like a spark issue?

ive check my vacuum hoses and nothing is cracked or unplugged. and the vacuum ports that are in use on the carb have their plugs in them. any suggestions to help me pinpoint my problem are greatly appreciated. and as i said. the engine runs fine if i move the high speed throttle valve. but if i use the primary (low rpm) one it just wantts to stall.