I've got an 85 Yammie 115hp (115ETLK) thst runs very very nicely so far. My only issue is that it smokes quite a bit. I'm using Mercury 2cycle oil at 50:1 and can't really think of any other issues. Any ideas?

IF you are premixing it will smoke. An engine only requires 50:1 at full throttle. At idle an oil injected engine is getting more like 100:1 and it goes up as the rpms go up. More rpms more oil. Too bad theres no other way to adjust your oil but 50:1 is the only safe way to premix. If it is still smoking at full throttle then I would guess you may have more serious problems, but lets hope not!!

So there's really no way around it at idle? Does one oil smoke less than another?

I'm not sure about one oil smoking less than the other but I really wouldnt worry about it just make sure you are using good marine grade oil.

I run a Yamaha too.While breaking it in ,I was told to go 50:1 and it smoked like a tar keel.After the break in period ,I'm now going with 100:1 ,and the smoking has all but disappeared.