you can do a simp-le okie leakdown test to see more clearly if it it valves or rings
you already oiled the rings so its more to hear the valves leaking leave a sparklplug out of 1 cylinder hence you are listening to the other
having the exhaust removed id best to observe and hear if the exhaust valve leakes
popping of the carbs or just wire the throttle wot and very gently prop open fully the slides
you can rotate the engine with a wrench on the crankshaft end
or shift it into top gear and rotate rear wheel
you cannot rotate the engine with the wheel in the lower gears
having an asistant do the rotating and hold your beer,is good, lets you here the hissing out either side
if the rings are leaking you will hear that hissing as well
very simple when the engine is coming up on comp both valves are fully closed and any valve leakage will be quite observable ,heard out the port or carb
but first adjust the valves ,no not totally needed , just make sure they have some clearance when the rocker arm is over the base circle any clearance is fine as long as it is not huge thats a bad sign and a small varience in valve clearance, has absolutely no effect on compression or the reading you will get
if the valves have a bunch of clearance thats usually an unhappy sign
keep going you must get it running first its completely idiotic not to
and or buy a running one
buy another one anyway in fact that is my number 2 suggestion hord them
the black gunk in the starter is quite normal just blow it out with comp air,not in your garage lol
98% of the time when a starter quits is because the carbon brushes have worn down so much that they are hanging up on their wire tail and then just skimming the comutater
real easy to deduce if this is the sitch
if so replace brushes and check comutater for being out of round spin it in your lathe or on v blocks and put your dial indicator on it
or just take it to the local generator/starter rebuilding shop ask them please would they check and or clean it up
they will have brushes too in fact they can "rebuild" the unit its no dif than any car starter
they can test the whole thing as well
but yeah get that turd running,get it out and ride it ,dont make the big mistake