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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
