I've recently done a carb rebuild/clean on a carb to a Mercury 1979 20hp Thunderbolt ignition. The motor wasn't running all the smoothly before the rebuild but seems to be afterwards.<br /><br />My problem is that the motor runs perfect with the idle mixture screw lightly seated. Straight after a quarter to half turn of the screw the cylinders start overloading with fuel and blue smoke billows from the exhaust. Before the motor need approx 1 3/4 from lighted seated position.<br /><br />I've found out that the idle tube isn't screwed in 'tight' but the 1 1/4 turns from lighted seated (mis understanding on my part of the selco book). Would this have a large effect?<br /><br />Any other suggestions?<br /><br />The fuel screen was full of dirt and paint bits?!! The whole carb was squeaky clean after the rebuild. All fuel lines have been checked, a 1 week old fuel mixture but does have slightly too much oil maybe about 1:40
