amsoil is good stuff, i definitely second what everybody has said.

 

Very well put ss97. You are right that it isn't only synthetic oils with friction modifiers but synthetics more commonly have friction modifiers to help improve motor life. I have used several types of non-synthetic oil over the years and never had probs but I have tried synthetics twice in atvs which both cause clutch issues (with exception of the syntheic amsoil atv oil I'm using now). That is why I pointed it out that synthetic oils could cause clutch problems due to my own experinces, where I haven't had issues with more conventional oil but only heard of issues from others.
Amsoil rocks!!!!

 

AMSOIL 0W-40 Powersports oil here... great stuff! I'm sure it would work as well in a Yamaha.

 

We have been using Amsoil for about 10 years in everything that we own. Grizzly 660 and now a Grizzly 700, Z400, two Harley Fatboys, 2000 Chevy Silverado (brought it home from the dealer, drained the factory oil the same day and have been using Amsoil ever since. Just turned 80,000 miles two weeks ago.) and an 03 Toyota 4-Runner. Amsoil is a bit more expensive but great stuff and well worth it.

 

<div class="FTQUOTE"><begin quote>Originally posted by: TLC

Is there such thing as a bad Full synthetic oil? The wost Synthetic oil made is better than the best conventional oil made,I would guess.</end quote></div>

Sorry I did not mention it. I meant motorcycles grade synthetic oil which are designed for wet clutches.