Mark---It's possible that the carb you think is lean could actually be
rich, based on the blackened spark plugs. There is a cross over in the
intake manifold that allows fuel to supply the other side. I would
remove both air valves and measure how far the needles are up in their
sleeve, to confirm this. You can mic the thickness of each needle as
close as possible to the bottom of each valve. They should be identical,
(i.e. .090) if both carbs are adjusted to share the duties.
Another less exact way would be to screw both needles up into their air
valves, to full rich. Note how many quarter turns it took to "bottom
out" the adjustments. Then turn them towards "lean" one full turn each,
to start with. Do quarter turns equally, from there.
I believe 1/4" lift to be too much when checking the mix. Try 1/16" lift
and see what that produces.
Next, operate the throttle by hand, while looking into each carb. Both
air valves should rise equally. Be sure the linkage turns both halves of
the throttle shaft equally. Check also the diaphragms for fit and
wholeness, since it is vacuum that raises the needles.
What prompted you to start working on the carbs? Isn't this the engine
that got you across the mainland?
After checking/adjusting the above, write back if the engine still runs
ratty, and you believe that the carbs are now set right.
Dick
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