I've run into an interesting dilemma with the '74 CBB.
It all started when I decided to make a reasonable effort to
make it idle. So, I followed the accepted standard procedure of pulling
both carbs, adjusting the floats, setting the jets, reinstall, top up
dashpots, etc... It still didn't idle as smooth as I would like, but
that could likely be cured with some further fiddling.
Unfortunately, I also decided to pull the rocker cover and have
a look at the rocker clearances. Found a couple on #1 and #4 that were a
little tight, so I reset them to .015. The jam nuts didn't go up as
tight as I would have liked, but I thought they were okay.
I was wrong - it only took a couple of miles of driving before
they backed out far enough that the valves stopped opening. Much popping
through the carbs (sounded like a bad exhaust leak). Managed to get
within a couple of blocks from home before it quit. Pushed the rest of
the way (all downhill - lucky me).
Pulled the plugs - compression check shows 145 lbs across the
board. Pulled the rocker cover and discovered the threads had pulled out
of the jam nuts I had adjusted and let the screws run out. Bought new
jam nuts, readjusted, replaced rocker cover, reinstalled plugs and
wires, ready to fire it up.
Nothing. Checked for spark (ok). Pulled fuel line leading into
front carb to check pump - pump is ok. Pulled air cleaners and looked
for fuel - throats were dry. Sprayed in some starting fluid - engine
fired, died as soon as starting fluid was gone.
I'm now thinking that the float valve is plugged, so I pulled
the front SU. Took off float cover - gas in float chamber. Blew through
fuel inlet - no obstruction. Pulled and blew through jet - no
obstruction. Rechecked float clearance - all is well. Replaced jet,
reinstalled float cover, and called it a night. Will perform same check
on other SU tonight.
However, I don't expect to find anything wrong with the other
SU. I also have a nasty feeling that I've missed something that's really
causing this. Does anyone have any suggestions on what I should try
next?
For the record, the car was de-smogged by a DPO, so there's no
air pump or gulp valve. It still has the steel tube between the two
carbs (don't know what it's for) and the vents to the charcoal canister
still in place.
Dan Pockrus
'74 CBB
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