Re: '76 model Johnson running problems
Yikes, that explains a lot. That slow speed mixture needle shaft (and pointed end) should be in one piece. From what you're describing, the tip, or point has broken off of the main shaft and is stuck in the hole (seat). Usually I'll unscrew the needle a bit watching the tip retract from the hole and then turn clockwise to lightly seat it again. I watch the tip for any rotational movement indicating a possible bent tip. The tip does not have to be needle sharp, just pointy enough to enter the hole and seal when tightened with light pressure. You can remove the needle and inspect the tip. With the needle completely removed, there shouldn't be anything protruding from the hole (needle seat). Actually, the needle seat can have the same taper as the needle tip. This insures a gradual metering of fuel past that tip to fill the chamber just beyond. Sadly, since you have already replaced the aluminum plug, you can't see the in and out movement of the needle tip. What you don't want to see is the tip that has a ridge around the tapered portion of the tip. This results from the needle having been screwed in too tightly. Fuel won't freely pass over this ridge and it makes the needle setting hard to adjust. Tips that do have this ridge can be dressed with a fine tooth file while turning the needle in a drill on slow speed. You would want to maintain the original taper angle while you dress it back to an original shape. Fine emory cloth would then be used to polish the taper to remove any file marks , if any.
So to cut to the chase (at last)....if the needle tip has broken off and is closing off the needle seat, no fuel will flow for the idle circuit (into those little holes in the chamber). As a side note, there are 2 piece needles...the main needle shaft with an interference fit tip. If the tip has separated from the main shaft it would not screw in and out as it should, like in your case, the tip would block the seat and the main needle be removable. The fix, remove the aluminum core plug and push the tip in, towards the needle shaft hole and let it drop out. The tip should have an O.D. smaller than the I.D. of the main threaded needle shaft hole. Others more familiar with that carb might jump in here to confirm the 2 part needle construction.
If it is the 2 part needle, try removing the needle and holding the needle shaft hole pointing down. Lightly tap the upper carb body at the core plug hoping to dislodge the tip from its seat and with luck it will drop out of the threaded hole. If that fails, try inserting a thin ice pick into the threaded hole and wiggle the tip from it's seat. That tip shouldn't be jammed in it's seat , unless someone tightened it down to hard. Under normal motor operation the needle isn't fully seated anyway, it would be approx. 1 turn or so open (off the seat).
Removing the core plug and pushing the tip from the seat is an option, but you'd have to have a replacement core plug handy.
As a permanent fix for the 2 part needle, I'd solder tin the main needle shaft end and while still hot, replace the tip and let it cool. I wouldn't trust any type of epoxy or glue for this application. The soldering fix is an extremely strong repair and basically permanent. Light burnishing of the surfaces to remove any oxide followed with a bit of paste flux will insure a good solder repair. A small propane torch will do fine and the solder will easily flow. After the tip is replaced, heat the tip a bit to evenly heat the junction and let it cool.
As a last thought, if the end of the needle shaft doesn't look like it broke off the tip and is basically a machined flat perpendicular to the shaft, its more than likely a 2 part needle....
