The manuels for the old bikes say to mix that way becuase back then they didnt have all the good synthetic oils like we do now. with a good oil like golden spectro, amsoil, and bel ray you can probably get away with 40:1

 

I use 20:1 and have no problem with fouling plugs. I have ran into some bad NGK plugs but have had others that ran for over 6 months and were only replaced becuase I had long since got my 1.50$ worth and figured its best to replace it before it does quit 5 miles from the truck. More lubrication is always better unless your racing for money or fouling plugs. If I ran something that said 100:1 on the bottle I would still run either 20:1 or just a bit less than it takes to foul my plugs. Some may foul plugs easier than others becuse of different jetting or weak spark. I would have probably never tried 20:1 but the book said it so I started there and have not had a reason to go less.

 

If you can find it, I had my best luck with Castrol 2-Stroke oil.

 

it does get costly to run 20:1 tho.i may change to 32:1 because of the costs.if i run like a 25,26:1 it would richin my bike out wouldnt it?id feel more comfortable if the plug was a dry black than a brown.so it has a little room for temperature changes and so fourth.