Which engine/gearbox oil should I use?

[mal68]

Hi, just looking for advice on which engine oil to run in my 2003 Suzuki LTF500, its been run since new on a semi synthetic (can't remember brand), and changed regularly at the dealers....but I was just wondering what to use now? Its the 5 speed high/low manual one...Its done high ks, but engine starts instantly, runs smoothly and dosen't smoke...but I often wonder if I'm hearing piston slap if it gets laboured...hopefully not. I was figuring the semi synthetic may be a tad thin? The gearbox is also "crunchy" between shifts sometimes, was wondering if a specialised motorcycle mineral oil would be a better alternative? I read somewhere on the net the LTFs were prone to piston slap.
Any advice gratefully recieved, I'm a bugger for "over servicing" with oils etc, so it will be getting changed regularly...also what tyre pressure is best for sandhills? Cheers for the input!

[crazyxr250rider]

Motul 3100 10w40 would be fine for your quad, I think suzuki recomends 4 to 5psi front and rear