Welcome LT80 newbie.
The oil injection: there should be opil drip out, it is slow. Removing the oil inj. and running pre mix is the best.
Yes the screw is the idle adj. It should idle fine but after sitting, it may need some running to get the old gas and such out.
100 isn't the best but should be good enough for now. I've seen alot worse and run.
And you did remove the pilot jet and make sure the lil holes were clean
You also cleaned the gas tank out.
You also tried it with the petcok on prime to see if the petcock/vaccum isn't the problem.
Pulling at idle may point to a clutch problem. I'd maintenence the clutchs while you have the clutch cover off disabiling the injector. LOL
You'll be checking the rollers for flat spots,hard grease,wore variator (where the rollers sit).
That'll keep ya busy.
2000 GNC 5N\
2001 GNC 9N \ 40+ class
2004 GNC 9N /
2014 rock crusher "GO tortoise GO!"
2016 Byrd Rooster
Father of the "11" time National champion,and worlds fastest woman ATV racer
A few fast LT80's
250R~300cc's
300ex
350 Rancher
Kymco Mongoose
Survivor of the 12 Hours of ATV America 04 and 05