Read through all the replies, all good advice, and here's my funky addition that may or may not be of use... What was the AIR TEMP OUTSIDE? I have found that with all else working, monojets seem to like to ice up if the hot air stove from the manifold is missing or rotted out. Really. If it starts and runs well above about 5 degrees above freezing and below about 5 below, but stumbles, stalls, and runs like crap between, and if you shut it off for 5 min then and it restarts and runs smooth for another 5 before it starts acting up again.... There is quite a temperature drop as the air speeds up through the venturi, and it will freeze the water vapour in the air, stick to the bore and mess up the actual venturi effect, and block the idle passage too. you can keep it running with lots of throttle of course. I think below about -5C (27F) that the relative humidity is too low to sustain the effect because mine would clear up about then. Took me a year to figure that out, and since have run into it on 4 seperate trucks - each one ran perfectly again with the hot air inlet repaired.
