Switched to conventional oil, bike now runs rough.
 

So this is my second oil changed since I bought the bike about 4 months ago. I used full synthetic the first time and the bike ran real smooth. About a few days ago I changed the oil with castrol 4T and now the bike has alot more vibration. The temperature climbed to 235 today in traffic quickly. I've rode the bike all summer and the temps never went pass 230 when I ran synthetic. The bike vibrates alot more when I'm riding and while it's idling. I can feel it the most around the handle bars and my legs. Does the f4i like synthetic only?

Many here run Rotella T dino 15w40 w/ great results. Its avail at walmart & budget priced.

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Has nothing to do with the oil.

I've been running Rotella 5W-40 synthetic since about the time I joined the forum. Excellent oil, not just for bikes. At around $25 gallon, it's a win win situation.

I've heard that it's ok to go from regular oil to synthetic but not to go from synthetic to regular oil, i think i read that on the ninja250 forum

Once you go synthetic you in theory can go back. But the more the two oils combine, the worse it is. More so if they're different weights(sp).