What kind of oil do you use and why?

I'll open up the can of worms here. That would be "afraid"..Anyhow, I'm a big fan of synthetic oil, and my brand of choice is Amsoil, specifically their ASE, which is formulated for small engines like all the lawnmowers, snowblowers, gen-sets, etc.

You've been around the net, I see; funny, benski.  I take the opposite tack from you, and in my old Tecumseh flatheads (and other old small 4-strokes like tillers) I use straight 30wt. Since automotive oils (but not the diesel oils) were recentlly reformulated to eliminate a supposedly environmentally unfriendly zinc compound, at the oil change I now add some supplemental zinc by Rislone. I use this in any car or truck that is any older than the newest generation made to handle the no/low-zinc oil. And occasionally when gassing up, I put in a little from my can of 2-stroke premix fuel. In the old days some of us used to periodically add a little "top cylinder lube" to the fuel. This was essentially an easy-mixing sort of 2-stroke oil, Bardahl being a popular brand out here; others swore by Marvel Mystery Oil. The idea was to get a little extra lube to the valve guides and to rings. It can't hurt, might help, but don't over-do it or you'll have a 2-stroke blue haze trailing behind your tractor.

Where I believe this use of some 2-stroke premix in the fuel IS very important is when starting an engine that has not been run for months or years, something I do in addition to pulling the sparkplug and shooting some oil in the hole, after which I turn the engine over for a while with the plug still out and grounded. Put some of the 2-stroke premix in your startup primer-bottle as well (better than an ether-type starting fluid when dealing with a long-unused engine). Give the poor old engine every chance, I say.

Okay, benski, now you and I can stand back and watch the fur fly.

Sae30 in the summer 5w30 in the winter. I have found sinthetic oils in older engines tend to be a little smokey due to the loose tollerances. But if I was to do a rebuild I would prolly go with a senthetic. But until then I stick with conventional