merc 1150 idle mixture screw setting. more info!

[monk-monk]

I posted a thread about this topic back on April 18th and I learned a lot from the replies and was very helpful! BUT, that only raises more questions....Rear Admiral Chris1956...Im clear on the tweaking of the idle mixture screws, used to do this with a vaccum gauge on my Holley carbs...same principle, good to know...BUT, Chris1956...you say the bottom carb runs the richest and the middle carb is slightly leaner, and the top carb then is the leanest...Am i interpreting this correctly and if so, my question is: What carb do i tweak on first, top-to-bottom, or bottom-to-top...I would like to ask if this Rich, richer and richest is just the "nature-of-the-beast, but with an idle mixture screw available, I can't see that being the case, so are you saying to "richen" it up from the bottom up or what?

 

[Chris1956]

Re: merc 1150 idle mixture screw setting. more info!

OK, My procedure to set the idle mixture involves three steps:

Set the idle mixture screws each to 1-1/2 turns out from lighty seated.

Adjust the mixture screws for fastest an smoothest idle.

Richen the mixture just enough to accelerate smoothly.

Eventhough you start with the same initial idle needle setting on all three carbs, the mixture on the bottom carb is still a bit richer than the mid carb, which is a bit richer than the top carb. Now you adjust the needles to get the best idle. You will likely see that you will lean out the bottom carb a bit more than the mid and top carb. Now the mixture is close, bit likely still richer on the bottom carb.

Now you need to richen the mixture to get good acceleration. Since the bottom carb runs richer, you may not need to richen the mixture as much as the top carb, or at all