John,
Sounds like Saskia is having a few teething troubles with her new engine and
everything!
There are a few causes of the idle not always returning right down where it
should. My first point to check would be that the mechanism isn't catching
at any point, possibly in combination with insufficient/too weak springs to
return it. Fiddle with the mechanim (all points from the pedal to the carb)
and see if you can feel it catching slightly at any point of the movement.
Make sure that you have all the springs you should - Daffy (who I assume is
correct, but couldn't say for sure) has 3 - a shorter one by each carb going
upwards to the bracket that also holds the throttle cable, plus a larger one
heading downwards and terminating at a bracket clamped under one of the
manifold/downpipe nuts.
The next possibility is a little more serious - worn throttle shafts in the
carbs. This can allow extra air in where the throttle shaft enters the
carb, so raising revs. With this new engine, were the carbs re-conditioned
or re-built? If this is the problem, I believe the only solution is new
shafts, in combination with having holes the carb bodies drilled out further
and inserts fitted, so the shaft is a close fit again. The drilling needs
doing professionally, to make sure the holes are properly aligned.
The second problem can be checked for by spraying something (carb cleaner??
not sure) at the point where the throttle shafts enter the carbs - revs will
rise (I believe) if the spray gets sucked into the carbs.
A third possibility is the over-run valves - little poppet valves in the
throttle disc in the carb, fitted to later 1500s to improve emissions when
the throttle is shut off sharply after being wide open. I have soldered
mine shut; others have simply replaced their throttle discs with the earlier
ones without this (pretty pointless) feature.
As for the oil light problem... hmmm... don't entirely like the sound of
that. I would first of all ask what oil was put in there. Nevertheless,
even with much too thin oil, I wouldn't expect the light to come on, unless
the bearings in this engine are badly worn. It is possible that the oil
pressure sensor in this engine activates at too high a pressure, but without
an oil pressure gauge it is hard to know exactly what your pressure is.
Maybe you could swap the sensor and see if the same thing still happens?
Hope some of this helps!
Richard & Daffy
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