Hello. I'm new to here so please bear with me if you've heard some of this before. I recently switched out a 4cyl merc with a straight 6 merc. Couple of questions here. First, I canot find the serial # on the straight 6. By the looks of it, i would guess late 60's early 70's, and it has the old wire colors for the harness. I switched the harness over( by this i mean i had to cut the plug off the newer 4 cyl. and wire it into the old harness) and everything seems to work fine but my tach reads 3000 at idle and buries it at any over half throttle. So these are my two questions, how can I find year of new engine I put in and what could possibly be the prob with my tach. Any help appreciated. Thanks.....
