I recently purchased a used '07 Shadow Spirit 750DC but dont have the manual for it. Someone said to use 10w-30 but some other site said to us 20w-50. As the bike has only 2100mi. I was looking for something synthetic. My next option is to consult a dealer but they will probably try to sell me there very expensive oil or something. any help is appreciated.  

I have the exact same motorcycle...purchased new in April '07. The manual says to use 10W-30. The 750DC is a great mid-size cruiser. Much better, in my opinion, than the newer model. I like chain drive, dual carbs. Happy riding!  

Thanks, Coach! I'll be sure to give it a try but did you use synthetic or conventional? Automotive or motorcycle specific? I'm leaning towards Castol Syntec 10w-30 but am interested to know what other riders are using.  Thanks!  

You need to use motorcyle specific oil. Automotive oil will make your clutch slip.  

I use Honda's brand of 10W-30 mineral oil. It's not cost prohibitive and I know its compatible with the bike.  

Cool, Thanks for the info. I really wanted to get this right.  

On the oil front, when an oil says 10W-30, the 10W is the winter rating (10W is tested at -25C, different temps are used for other W ratings- see http://en.wikipedia.org/wiki/Motor_oil for details ).

Now, that affects startup, and ALL oils thin as they heat up. The 2nd number says how the oil flows compared to a reference standard at the same operating temp.

If you run a "thicker" oil, it doesn't run quite as freely. It provides a little thicker layer of oil on the parts, but, it takes more energy to move the oil out of the way. Too thick, and it could cause damage (eg imagine using gear lube... 90 weight).

I'd break in the engine using factory specs, and if I thought the engine was noisy (for no reason), I might consider using a heavier oil, you can swap it out for $20.  

What oil is recomended oil for a '05 Suzuki C50T....I just put in a 20/50 brand name automotive oil in it and my buddy nearly had a heart attack...i have done this for 30 years on all my bikes.....did i miss something?  

The reason for your friend's concern is car oils are getting slicker, and most motorcycles have a wet clutch (fed by the oil in your crankcase. 30 years ago, we were comparing SD vs SE grade motor oil. I think they're up to at least SJ, and each time they change it, they make it more protective for the car engine (not necessarily the same requirements as a bike.

In some cases, people have had their clutches slip after putting auto oil in the bike.

BMW went as far as putting out a tech service bulletin on the subject.
http://www.gunsmoke.com/motorcycling/reviews/sj_oil/index.html

Or, if you want the complete explanation, you could check out this site.
http://www.wingworldmag.com/archives/november2005/magazine/article/OilStandards.html

Hope this helps.

BTW, I run motorcycle oil in my bikes. I figure even at 9000 miles a year, that's 3 oil changes, and the best I could save is $40 a year.  

HI;   I use 20-50 Mobil 1. I have a C50T 05. I got it from the dealer. They said that it would not make the clutch slip. It is ok for warranty. I have  just over 18K on the bike and no troubles. I run the crap out of this bike. Ride often... scruffy