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???? Not understanding the question. How have you established it is running lean? At idle or at full throttle? If at idle (sneezing), simply give the needle a tweak toward rich. If at wide open throttle, that is controlled by the fixed jet in the bottom of the carb bowl. That must be absolutely, positively clean, without any trace of dirt, gum, varnish or whatever. But don’t go reaming or drilling it out. Oversize is just as bad as undersize/dirty.
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If it’s idling lean, turn the mixture screw out a bit (CCW) to richen it. This low speed needle should be set slightly rich from smooth idle anyway to help prevent stumbling when opening the throttle. As mentioned, the high speed mixture is nonadjustable on this motor and is controlled by a fixed orifice jet in the carb bowl.
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Maybe the first thing that needs to be said is that turning the adjustment all the way IN, LEANS it. Turning it OUT, richens it. Maybe some of your other engines (like Neptunes?) had carbs that worked opposite of this one? Some do. I agree that the question needs more clarification. When, and with what symptoms, does it run lean, to your knowledge? While you chew on those thoughts for awhile, another couple of thoughts comes to mind: As Fleetwin established awhile back, 6 hp OMCs have been built with at least three different high speed jet orifice sizes, for reasons unknown to us mere mortals. You haven’t mixed and matched carburetors along the way, have you? Also, how is the throttle pick-up adjustment set? The throttle plate shaft ITSELF, should just begin to move as the cam follower lines up with the mark on the cam on the mag plate. Sometimes there is considerable slack in the mechanism that needs to be taken into consideration.
Long live American manufacturing!
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and if it works don’t go looking for a fix,
Joining AOMCI has priviledges 🙂
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You say at the end of your post that it runs “GREAT!”.
If your only issue is “the needle is turned nearly all the
way in” what is “nearly”? 1/4 turn out? 3/4 of a turn out?
You say “The carb has been cleaned”? Just sprayed down
with some cleaner and wiped off or disassembled, soaked
in an ultrasonic tank or in carb cleaner and a rebuilt kit
installed? Cleaning and rebuilding of a dirty carburetor
will often require a change it the mixture screw setting.
Tubs.A "Boathouse Repair" is one that done without having tools or the skills to do it properly.
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So you are worried about the physical position of the needle, not the actual rich/leaness of the result? Word from here is don’t worry about it. As long as it is responding to adjustment, it should be fine. Wit motor warmed up and running at slow idle, turn the knob toward lean till it falters or sneezes (or quits), then back towards rich till it regains smooth running. Further turning toward rich should make it run rough. Proper setting is somewhere between sneezing and rich roughness. Feel free to tweak it a hair till you are satisfied. Then leave it alone.
BTW, the slow speed needle is just that–for slow speed. The fixed-jet orifice plug in the bottom is what controls the mixture at higher speeds.
Most will agree that a tad more oil for break-in of new pistons & rings is OK. Don’t go crazy with it though. 24:1 MAX.
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