I have an 18 hp craftsman rider. It has spark and is getting fuel. It barely turns over, and then only one compression stroke. If u remove the plug it whirls over fine, a friend said the vlaves need to be adjusted but I don't know how. And thoughts?

Hard to tell without the make of the engine. Also can't make any guesses without a model #.

For some of the overhead cam Briggs engines, you rotate the piston 1/4" down on the power stroke (intake, exhaust, compression, power) and use a flat feeler gage under the rocker's and adjust each valve for the proper clearance so that the feeler is snug when inserted and lock down the lock-nuts. Clearances should be able to be found online, otherwise it's available in the repair manual. If briggs its, Home - Briggs & Stratton or you can use Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears PartsDirect | SearsPartsDirect.com for breakdown info.

Briggs stamps their blower housing (impossible to read) with a model and type number. From there, breakdown manuals are free, but service manuals are not.

This is similar, but unlike the way car valves are adjusted.