yes 1/8 turn lean it needs from factory setting.

I run a different exhaust, OS/hatori and ES pipe. I have never had any trouble whatsoever with this combo, and I also run at least 16x13 to 17x12 prop.

if you run within these parameters and still have trouble, then you may have a rare "bad" OS 140RX.

One note. The factory low end setting is rich, so if it's loading up, then you need to lean it out. This engine likes to be a little lean on the bottom end. Try this: Crank it and run it up to full power. Let it heat up to operating temp, and then drop it to idle. let it idle for about 30 seconds. Then run it up. if it does ok, then you're good to go.

If not: Do the above and drop the engien to idle. Now let it settle for about 15 seconds. With a pair of hemostats or pliers, pich off the fuel line to the carb. The engine should increase SLIGHTLY in RPM and then die. if it dies suddenly, it's lean. if it jumps up really high in RPM, it's rich. Adjust from there.

Try that and see how it goes.

-Mike