Is there a (auto) compression release on an 18 HP Briggs (single cylinder) to aid in starting? Sometimes I have to manually turn the engine past the compression stroke to get it to turn over. Battery is good because I have the same problem when it's hooked up to my truck battery.

A large Briggs OHV should have an internal fly-weight setup that holds the exhaust valve open a bit until RPMs increase. Maybe check the valve lash. That being out of spec will effect this system.

Joel

Actually I think is holds the inlet valve open on this particular eengine, when starting make sure the throttle is open, also the valve clearance needs to be set correctly for the release to work correctly.
Here is one reference to it, but there are many others with details of how to do it correctly, and many references of people replacing battery and starters to find the same thing and then adjust the valves and all is good.http://www.mytractorforum.com/showthread.php?t=32134

valve clearance needs to be set correctly for the release to work correctly ..had the same problem and it is an easy fix