Just got finished with one that displayed about every symptom you can describe...
It would start but only idle... then sometimes idle for 5 minutes, or just die, Giving it throttle would kill it, as if the main jets were plugged.. adding choke a bit would help and speed it up a bit,, then adding choke would not help and slow it down a bit... then it would flood, then it would starve for fuel,, then there was no spark, but then there was plenty of spark.. Plugs would be wet, then plugs would be bone dry...
and the symptoms kept changing... every few minutes... I had this one sitting on a trailer and would "pick" at it a few minutes every day, as I had plows and other equipment on the trailer behind it...
turned out.. after going down the yellow brick road.. rebuilding the carb multiple times, rodding out all the ports and passages, checking fuel flow, cleaning all the filters and screens,, bypassing the ignition switch, replacing the coil, measuring the points resistance... that measure zero or near zero... all to no avail.....Measured the resistance from the distributor base plate to ground to make sure the internal ground strap was good..
it was the dangity dang Chinese points... they would work, giving a somewhat good ground to the coil, then change to high resistance, then work again... I changed them out with a new set of "junk" points from a local supplier, and mysteriously all the weird symptoms went away.. suddenly the main jets were good, fuel delivery was good, coil spark was good, the jubilee ran like it was brand new....
and now in a couple of days, couple of weeks, or couple of months,, it will start acting up all over again do to sub standard points.... Got several sets of 'merican points coming in a day or two.. will put that problem to rest.
cleaning the old points did not change anything, light cleaning, then with alcohol, then with rough paper, then even a hard points file, with new surfaces,, did nothing... So.... though I would pass this along.
At least this one is well serviced going to the customer. I am amazed how many times the symptoms changed..