I found a recommendation for older carbureted bikes of 1 ounce of Pennzoil TC-W3 marine 2-stroke oil per gallon. The claim is that today's gas is refined to have so little light oils, and with the addition of ethanol, that it is too 'dry', whatever that means. Adding a small amount of oil keeps the carbs clean, and works as a top oil for the intake valves, they say. I tried it in my old CB450, and we'll see how it works out the next time I drain the carbs.
been doing that, TC-W3 for the past 8 months. runs better and slight increase in mpg 1-2. the ratio is key to see great results.
much info here and how it was tested to work. I also use it in my diesel, where it also works very well.
http://www.ls1.com/forums/f48/been-testing-oil-91206/