I changed my oil yesterday and actually used Suzuki oil instead of Valvoline Durablend 10w40.....Man what a difference! The clutch is more responsive and the whole engine seems to run better. I'd heard that you should'nt use car oil in bikes with a wet clutch but did anyway, because I'd heard other people say that it doesn't matter. It sure did in my bike . It's much quieter and smoother running also. I had noticed that whenever I changed the oil before the clutch would feel funny for 50 or 60 miles but this was an immediate difference I could tell as soon as I squeezed the clutch to put it into 1st gear. it didn't " pop" like it always had before.

Amazingly not much. I think the filter retails at 5 somethin and the oil @ 3 bucks a quart but I get 20% off retail because we ( my car dealership where I work in parts) trades with the Suzuki dealer at 20% off so it works out pretty well. I thinkl I paid around $12.00 for the filter and 3 quarts of oil.

You felt the diff, not because the Suzuki oil is good, but because what You had in the bike was bad ! If You don't believe me, please check what is writen on the Suzuki oil bottle.
I can tell You- " 4 CYCLE MOTOR OIL " /unless you put some synthetic oil/. 4 cycle motor oil doesn't mean motorcycle oil. You actually put a regular Suzuki car oil, sold by the motorcycle dealership. Check to see will You find anywhere on the bottle  mentioning that this oil is designed for motorcycle engine !

And as far as the oil had been using being bad, it happened only after I changed the oil not after a period of use.