[TR] TR3. Fuel mixture too rich.

[Randall]

>  The rear piston didn't offer
> the same resistance to being manually displaced upward. It was easier to
> push up, and when I let go of it, it fell more slowly down and not with a
> metal to metal click - more a soft noise. However, when I removed the
> damper, it fell quickly and with the same "clack" as the forward carb.

Sounds like a problem with the plunger.  What happens if you swap plungers
front/rear?

> The trouble is, that even with the mixture adjusting nut screwed
> totally upwards it's still far too rich.

Several possibilities.  One is that the float valve is leaking a bit, and
letting the fuel level go too high at idle.

Another is that the jet and/or needle are worn.  This can be almost
impossible to detect without special tools, easiest diagnosis is to replace
them with known good ones (for example, swap with the other carb).  Even
brand new components are sometimes wrong.

Also possible the carb is not assembled properly, or the upper gland is
damaged, etc.  There is a brass sealing washer between the upper half of the
jet bearing and the carb body that is sometimes left out and can allow fuel
to bypass the jet and leak into the throat.

But first you need to solve whatever is keeping the piston from landing with
a click.  It's impossible to set the mixture correctly if the piston doesn't
move freely, as any binding will change the air velocity through the venture
and upset the mixture.

As a side comment, on my TR3A carbs (now mounted on the TR3), there is
enough play in the fit between the domes and the body to affect the needle
centering.  To get a repeatable position (so I can R&R the dome without
having to recenter), I lightly turn the dome clockwise against the screws
while tightening them.

-- Randall