First off, many thanks to those who wrote (mostly off-list) with
suggestions and temperature info.
I solved the problem so for the general interest of the group and the
archives I feel obligated to let you know how it panned out.
As mentioned in the first post I suspected the float valves and the fuel
pressure. The float valves, which functioned well before the engine and
carb rebuild, were the earlier gross jet type (about 12 to 15 years
old). Yet, I was getting too much gas at the front carb, sometimes
overflowing at the needle jet. I tried a variety of float valves at my
disposal including the spring loaded metal tipped type that came with
the rebuild kit but still the motor didn't run with any power and the
front exhaust manifold was very cold (overly rich)
I switched the working gross jet valve of rear carb with the spring
loaded valve of the front and was able to switch the conditions i.e. the
front three cylinders were firing well and the rear exhaust manifolds
were cold. At least this helped to narrow down the possible causes.
I double checked the fuel pump settings since I had rebuilt that also. I
took it partially apart again and reset the diaphragm. This time I made
sure to move the blade above the points before setting the 'no rocker
throw-over' and then backing out 2/3 of a turn. I also changed to a
larger capacity fuel filter just after the pump thinking that might
reduce the some surge pressure from the fuel stream.
I spent a long time working over the fuel float linkage to make sure
they operated freely and cleaned the gross jets with solvent and air
pressure one more time.
After a bit of carb tuning the motor is running well and external
exhaust temp readings about 1" from the head are within 10-15 degrees
(around 340 degrees F) after full warm up. Of course I did multiple
things at once so I can't pinpoint exactly which fix or fixes were
required and which were just busy work but maybe it will help someone
else out some day.
Cheers,
John
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