Jerry :
I think you've done plenty of tests, the rear SU is clearly running very
rich at idle.
As others have suggested, the problem may be the float valve. My first
suggestion is to remove the chamber lid, remove the pivot, arm, and needle,
then hook it back up to the fuel line and crank the engine a few
revolutions, to flush it out with fuel. (It's going to splash all over, so
you might want to stick the lid inside a Mason jar or something.)
Reassemble the lid, and check the float height adjustment. Pick the float
out, and shake it to see if there's liquid fuel inside. Put it back
together, and try again.
Other possible causes are a leaking upper jet seal, or a worn jet and/or
needle. Replacement with known good parts is about the only test I know for
these. I'd suggest changing both seals while you have it apart, but you
could use the jet and needle from the front carb (swap them front to rear).
Change it's seals too. Make sure the spring and two little copper washers
are in the right places, but don't try to stretch the spring to improve the
seal.
Make sure the piston falls freely, and makes a distinct click as it lands.
Improper jet centering can cause it to bind just as it reaches bottom, which
will make it impossible to set the idle mixture, and cause the jet to wear
over time. With the damper removed, the piston should also rise easily and
quietly. If you can hear it rub on the chamber, it needs to be corrected.
It's possible the rear plugs are too fouled to fire by now, so you may need
to swap 1-2 with 3-4 again, after making the carb changes.
FWIW, I'm not a fan of Grose jets. The factory type float valve works quite
well, and lasts a long time. Mine have lasted longer than Grose Jets have
been on the market ... and every time I've been tempted to blame them for a
problem, it's turned out to be something else, like the rubber connecting
hoses slowly falling to bits internally. IMO Grose jets are a solution
without a problem.
Good Luck
Randall
59 TR3A daily driver
jgoulet@finning.ca wrote :
>
> Could the rear SU cause this?
> Can you suggest any more tests?
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