15W40 or something else? Synethetic or mineral?

[gtexan]

I have a bet & win 250, kymco.  The manual calls for SAE 15W40 for engine oil. 
I went to my scooter shop, and they carry 10W40, 10W50, and 20W40 engine oil.  They are all for scooter or motorcycles

I went to the local auto parts dealer and they carry 15W40 and synthetic 15W40.  All the 15W40s they carry say they are great for diesel engines

I purchased the Royal Purple, full synthetic 15W40 motor oil from Napa Autoparts.  Here is the website: http://www.royalpurple.com/motor-oil.html

Is that going to be OK to use? Or would I be better off using a 10W40 or 20W50 formulated specifically for 4 stroke engines? 
The Royal Purple says its for 4 cycle engines (is this the same?)

I'd rather use this as its much easier to obtain, and the one at the cycle shops are brands I've never heard of.  But I don't want to use something thaats going to ruin my engine

[kawzak]

I read you question abouts the Royal Purple oil. It should be fine, I think synthetics are better that regular petroleum based oils. I am sure others may disagree. I have gotten high milage out of engines with regular oil, I just like the extra capabilities of synthetic. I read where some members of this forum use Shell Rotella 15w-40,and you can get it in regular or synthetic. You can buy it from Wal-Mart. You can also buy Mobil-1 a full synthetic from the same place. Just remember to change it often. The manual says every 2000km, thats only 1242 miles.I think with the synthetic I will do mine every 1500 miles  (AMSOIL) Since the engine on mine only holds a quart, its  cheap insurance to charge it often. Just remember that if you ever buy a scooter or motorcycle that has a wet clutch you would need to buy an oil that is wet clutch compatable-these usually have a JASO-MA rating. Remember to clean the oil screen located under a cap/bolt on the bottom of the engine.

[walkguru]

i used the rottolla synthic oil.