Setting idle mixture screw on 1150 merc

[monk-monk]

Sooo...I just refreshed a rack of carbs for my 1150 merc...instructions i've read about setting the idle mixture screw are given as "ballpark" figures...1 1/4 turns out "or there abouts"...My question is, can i use an illuminated spark plug reader to accurately set my carb mixture screws? And i would like to learn more about how each carb delivers fuel to what cylinder...does the top carb just feed the no. 1 n 2 cylinders an the second carb feed the 3 n 4 cylinders...hows that work....I catch on quick....educate me...

 

[Chris1956]

Re: Setting idle mixture screw on 1150 merc

Monk-Monk, The trick to setting those carbs is that they need to be set lean enough to idle well, but rich enough to allow the motor to accelerate. You need to do it by trial and error, unless you are an expert.

I recommend you start and run the motor in the water until it is warm. Now adjust the idle needles a bit at a time trying to achieve the highest RPM and smoothenss. At this point the carbs are synched to the cylinders, but likely set too lean to accelerate. Try to accelerate (in gear). If it stumbles, open the top carb 1/8 turn and try again. Repeat with mid carb, and bottom carb as is necessary.

BTW - The bottom carb runs richer than the mid and the mid carb runs richer than the top carb.