confused what oil to use in old 2 stroke moped transmission

Apr 11, 2023
I recently got a 1982 Yamaha qt50 its a 50cc two stroke moped with separate oil for the transmission. It has a single gear with a centrifugal clutch. The manual calls for 10w30 4 stroke oil rated API SE. Initially I was thinking I could just put modern PCMO 10w30 and not worry about it because the modern oils are far superior to the spect SE oil from the 70s. However I began to think that car oils with friction modifiers could cause an issues with the clutch. so would that be the case? Also I've heard that API S rated oils aren't necessarily backward compatible due to them having less zddp and phosforus. Could that cause an issue in a old transmission? Also if I go with PCMO should I go with high milage oils to swell the old seals that are known to leak on them?
the oils I am currently considering are
1 high milage synthetic 10w30 car oil
2 shell rotella t4 10w30 (due to its high zinc levels and JASO rating)
3 ST 10w30 UTV oil (because its api sl and meets JASO ma2)
4 a 10w40 motorcycle oil


  • Screen Shot 2023-04-17 at 4.45.39 PM.jpg
    Screen Shot 2023-04-17 at 4.45.39 PM.jpg
    81.4 KB · Views: 26
is your application wet clutch? if so then jaso m2 is about the only thing relevant in modern oil to a 1982 moped.
I'm currently running Rotella T5 10w30 in a shared sump bike and it works flawlessly.

The T4 10w30 isn't MA approved either.
I just saw this thread...and my first thought was that this little scoot had a dry clutch but a quick search shows that's wrong, it has a wet clutch! So you will need to use an oil specified for wet clutches.