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The effect of disconnecting a vacuum connection depends on the size of the hose - the engine uses vast amounts of air even in idle, and a bit extra, air, a vacuum leak, makes little difference…
Idle will increase with hose size, some 30 - 50 rpms for a ‘normal’ vacuum hose - a large leak may interfere noticeably with fuelling as the leak bypasses the AFM. However, engine behaviour to an air leak may also depend on hose interconnections - and where the hose is disconnected, or the leak occur…
All vacuum operated devices are disabled by their vacuum hoses’ disconnections - so if the disconnections relates to the dist vacuum; the engine will react accordingly. In your case; if there is an interconnection between the cruise control, same or interconnected tap-off as the dist vacuum, it may have an effect…
Otherwise, a vacuum leak in itself will not be noticeable except for the idle increase - except for eventual interference with dist. To check eventual interference of the cruise hose disconnection - connect a vacuum gauge to the dist hose and observe eventual differences…?
As you are running the Pertronix dist I think the stumbling is related to that item. If the stumbling during acceleration is caused by ‘pinking’, the ign is too advanced by dist advance curve. The standard advance settings are given for the standard dist - and the Pertronix may require different settings and eventual vacuum connections…
If the engine otherwise performs at speed with the higher fuel consumption it’s difficult to see lack of fuel as a cause. However, a ‘regulated’ fuel pressure test will reveal lack of adequate fuel delivery…
Frank
xj6 85 Sov Europe (UK/NZ)
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As a complicating factor; the increased idle may in itself bring the engine rpms up past the stumbling point - though that is drawing a very log bow…