How can I figure out the orifice size of OMC part #309681 ??<br /><br />Problem:<br />I rebuilt a 1970 Johnson 9.5 that I roamed the georgian bay with in my childhood. I was talked into a new-old-stock OMC factory rebuilt powerhead that a company had laying around. The powerhead was a 1973 which has a different reed valve arrangement. It does not run right! If I optimize the low speed adjustment for idle it runs rough at high speed. If I close off the low speed adjustment, it almost runs perfect at high speed but obviously, it will not idle. In all other respects it runs perfectly. All ignition parts are new and have been checked and rechecked several times. I conclude that the high speed orifice is too large due to different characteristics caused by the difference in the way the manifold looks to the carbeurator. I located a replacement carb for the 73 but there was evidence of tampering around the orifice plug seal plug. The orifice inside is a .048, the same as the 1970. I suspect this is not the correct orifice either. The listed part number is from a 1973 Johnson 9.5 parts list. I have been unable to prove or disprove my theory let alone straighten out my problem. Any tips or insight? 