Fuel blockage or air leak would be my guess.
When you sprayed brake cleaner I assume you meant around the inlet to locate leaks and not down the inlet which would show little, don't forget it is inflammable

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Another thing you could try is locate the vacuum feed to the brake servo at the inlet manifold and temporary disconnect and blank off to see if that affects things as a air leak there can cause poor running , also some people have experienced brake servos rusted through giving similar problems along with a harder brake pedal and not able to stop so quickly.