Yes the gas comes through those small holes in the throat as it’s sucked into the motor, but how does it get from the the bowl up to the low speed needle? Older OMC carbs route the fuel from the bottom of the bowl through a passage up the side of the cast bowl, through a hole in the bowl gasket to the top of the carb where it goes to the needle.

I did that last night and, besides coming out the little holes in the carb throat, it comes back through the high speed metering jet. I took the high speed jet out and did that again and it looked like it was coming from around the brass tube that is the main venturi tube in the casting above the jet.

I just found an exploded view in an old 1978 Clymer manual (see below). It shows (see red arrow) that the brass tube has a couple of holes near the bottom and one more a little over half way up. The holes in the bottom would be sitting in gas as they are below the float level of the gas. The hole farther up may go to a passage in the casting to the low speed needle, but I can’t tell form the drawing – see the red arrow below. What doesn’t show in that view is that the brass tube is fully encased in a cylindrical casting coming down from the center of the carb top, and the main jet (called an orifice plug in the drawing below) screws into the casting underneath the brass tube. I can’t find a good way to direct pressure from the carb cleaner tube through any passage to the needle to force dirt out. Maybe I have to pull welch plugs which a newer Clymer manual refers to as "Lead Shot".

Problem I have is I can’t get the motor to stay running when I idle it down to backtrolling speed. It runs best with the low speed needle 2-1/2 turns out and that is a bit far and still not good enough (manuals say to start one turn out). Also – this 1977 carb linkage does not have the little adjustment screw on the throttle linkage roller-cam follower that newer models have – I may be able to get a better idle if I could adjust the min throttle plate opening ever so slightly – I’ve had success on late 1980s motors with this.

Also open to other suggestions to make this thing idle right – I’ve wasted way to much time on my friend’s motor!

A couple years ago I worked on a similar model for a neighbor that would not sustain an idle and switching from Champion to NGK spark plugs very magically fixed it. I already have NGKs in this one. It just occurred to me I could have a bad new spark plug – I’ll try another set. I’m about out of stuff to try! It runs really good at fast idle and above.
Thx
Dave

Thanks for the tips!
This is not a salt water motor, and it’s not overheating.
My friend just bought this and was told it hadn’t been run for many years, so past running history is unknown.

I totally missed in the diagram that the carb has a bearing on the low speed needle – never heard of that before – I’ll check that. Is this something I can see with a bright flashlight looking in when I remove the needle? or "feel" poking a stiff wire with a small bend on the end in there? if not, how do I check for it?

I’ll check compression too.

I’ve never removed any of those lead shot plugs either and hope I don’t have to

Here’s a thought that came to me last night – I’m wondering if it’s possible that at slow idle, one cylinder is dropping out, maybe from a week coil or corroded coil ground connection? There is visible rust/corrosion the bolt at the top of the upper coil and that has ground wires, etc under it. I had it running first in a barrel, then when I put it on a boat, the fast idle "seemed" good but it was runnin’ on one cylinder when I went to WOT. After running a couple minutes, I dropped to an idle again and back to the dock. I shut it off briefly and then took it out again and both cylinders kicked in and WOT was great,and fast idle improved also. I’m thinking maybe the corroded ground connection got "flexed" as the motor heated up and metal expanded, squeezing/flexing connections to the block making for a better ground and that may have activated the 2nd cylinder. I’m thinking maybe at a slow idle, the ground still isn’t good enough, and that cylinder kicks out? I’ve never heard of this before, and it sounds a bit far out, but I’ll take apart and clean up the ground corrosion under that bolt and see if it helps.
Dave