There are frequently questions asked about the proper jet or orfice sizes for different outboard engine carburetors.Below is a post about this from a different board. Jay Smith, the guy who wrote the post, owns Jay Smith Racing Engines in Dayton, Texas, between Houston and Beaumont. He's a real knowledgeable guy and I don't think he would mind me posting this here.<br /><br />c/6<br /><br />Hooty<br /><br />Motor jetting to a color <br /><br />Tom , <br />Since nobody has posted I will try and help. The plugs should be a "paper bag" color to be the ultimate in correct jetting. I don't read plugs as there are too many varibles involved, I have had good luck only reading the piston itself. I make a high speed pass and if the hull will allow it without back washing over the splash well kill it clean. Then I roll # 5 piston ( as generally # 5 is the hot hole on a Mercury and prone to burn if the mixture is too lean ) to bottom dead center and look at the piston crown on the intake side ( that will be the side toward the outside of the block ) with a bend o lite , the intake side of the piston at the intake port should be wet and look moist about the size of a quarter out toward the middle from the port. If the wettness is over across half of the crown your too rich and can lean down a bit. If it is dry and ashy in color your too lean and you need to richen up in a hurry. Maybe other people have different methods but this has always been the ticket for me. Some rely on pyros , I have found that when a motor is too lean a pyro will be too late in its report and the piston is already smoked ( a 2.5 Merc with stock stroke comes to top dead center@ 10,000 rpms at a rate of 120 times a second I'm an old man and I can't react that fast maybe some of the younger ones can but my incounters with a lean motor things just happen too fast ) also on MANY occations I have had customers motors be STUPID rich and the pryos are reading flame not egt and they continue to richen even more chasing thier tails. Also if a pyro is "coked" up" it will also read incorrectly . This is why I haven't alot of faith in the pyro system of jetting. I always tell my customers when I build modified motors to start off very rich and SLOWLY work your way to dialing in your jetting. And by ALL means don't listen to JOE BLOW as to where his motor runs best on jetting as EVERY MOTOR is different and what might run great on one jetting curve might cost you another trip to the machine shop and bank !<br /><br />Good Luck,<br /><br />Jay @ JSRE
