stumble/hesitation

Weak accelerator pump,, do a "search" , lotsa threads on that,..

A vacuum leak,, diss-connect all vacuum attachments,- plug em,, and see if it's any better.. put a vac guage on it, a lotta info will show up there..

failing that, "reading the plugs", and a compression test would seem in order,, and look closely at all the sp plugs as you take them out, keep them in order, looking for one that is "different"..

hope it helps