Went to drop the oil in my new TTR230 last week when I first bought it from the original owner and I noticed the oil poured out slow and super thick, not good. Lucky for me he had just had it in for its first oil change at the dealership and hadn't even ridden it with that crap in it. I replaced it with recommended 10w 40 weight oil, Castrol 4t non-synthetic as I have been using with great results for over 10 years and the course of lots of atv's and dirt bikes. I have a friend that was a former Air Force Captain that was also an aircraft mechanic who explained to me that the turbine engines that turned over 40,000 rpms used oil that was thin as water because it needed to circulate through many small ports very quickly. Same would apply for a dirt bike engine, oil needs to be able to circulate quickly because these are quick reving performance engines. I've also been a dirt bike and atv mechanic for many years now and have noticed that every EBC Dirt Digger clutch kit I've put in recommends not to use synthetic oil in the machine's with there kits installed. That I can understand because I have had a bike start slipping clutches back years ago with a try at synthetic oil. I use synthetic in my pre-mix on two strokes and in my truck motor but nothing with wet clutches. My buddy john raced GNCC atv races and used Amsoil for a short time, he was changing his friction plates out completely every second to third race with the synthetic and getting as many as 6 or 7 races when he used conventional 4-stroke motorcycle non synthetic oil. Others may have different experiences with oil brand and weight but just wanted to share what I have come to know having been a dirt bike and atv rider and wrench for over 20 years.