re:
"The float bowls take care of immediate fuel needs"
Huh? Are you saying everything will be fine until the float bowls empty out?
Carburetors--excepting the pressure type--require a constant fuel level in the
float bowls (it's not like flushing a toilet ;). Remember, the level of the
fuel in the jet is the same as the level in the float bowl. If the float bowl
level is being reduced faster than than it can be replenished because of, say,
a fuel delivery issue, you will be effectively running with an incorrect
mixture until the float bowls catch up. I'm not sure which way the mixture will
go, but since you'd be lowering the fuel level it would probably be equivalent
to raising the vacuum piston, which produces a momentarily lean mixture (the
'traditional' way to test mixture on an SU carb). A lean mixture on
acceleration would cause sputtering and coughing, which is why carburetors have
a) accelerator pumps (constant venturi carbs) or b) vacuum piston damping fluid
and springs (SU carbs).
This is why getting the float levels set correctly is critical on any
(non-pressure) carburetor, and why needle (or ball) valve operation is also
critical. The proper operation of any carburetor is all about having a correct,
constant fuel level in the float bowl(s) and all the other parts properly
adjusted with respect to that level.
bs
--------------------------------
Bob Spidell - San Jose, CA
<snip>
Sounds like fuel delivery (acceleration requires more fuel than steady
cruise).
<snip>
I don't think it is a fuel delivery to the carburetor problem.
The float bowls take care of immediate fuel needs. A weak fuel pump or
clogged fuel filter would evidence themselves by the car being able to
accelerate to a certain speed (by consuming fuel already in the float
bowls) but not being able to maintain that speed (because fuel was being
consumed faster than the float bowls could refill).
On the other hand, it could be lack of sufficient fuel delivery
between the carbs and the combustion chambers.
- Bernie Johnsen 1967 BJ8
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