RE: OS .15 Steel Fin?
Strange, my OS-702 muffler (about 1968) has no pressure tap, just the bushing for priming. The tap in the back cover plate requires a check valve, the tap in the case below the carb doesn't, but both are for real pressure tanks and a regulator (like [link=http://www.rcuniverse.com/forum/fb.asp?m=8550127]this one[/link]) would be needed. At least I thought so. [link=http://www.osengines.com/history/ostimeline03.html]http://www.osengines.com/history/ostimeline03.html[/link]