At 10:05 PM 9/18/2006 -0400, Bill Wilkman wrote:
>I recently had my MGA's engine rebuilt .... new Aldon/Lucas
>performance distributor. The vacuum fitting on the old distributor
>was designed for a metal vacuum tube threaded into the vacuum
>advance and the carburetor.
This is actually a tube with a straight end. There is a small metal
ring called an olive, beveled on the outside, which fits snug on the
tube. Over that is a flare nut which presses the olive into the neck
of the threaded fitting on the vac advance unit. The tapered
surfaces and the end squeeze conspire to compress the olive onto the
tube for a tight fit.
>Mid-way in the stock metal vacuum tube is an oblong metal chamber
>through which the vacuum line extends.
The tube does not go all the way through, but connects on both ends
of the bulb. The bulb is full of wire wool and serves as a fuel
separator. When installed the bulb should stand on end with the
lower end connected to the carburetor, so any liquid fuel collected
in the bulb will run down to be drawn back into the carburetor on the
next vacuum cycle.
>The new distributor is designed to make use of a press-on hose fitting.
Typical of later model MGB parts. You can cut off the end of the
tube near the vac unit to remove the olive and the nut. Then connect
the tube to the vac unit with the right angle rubber conenctor used
for the later model MGB.
>My question is this: Is the oblong metal chamber necessary, or can
>I just run a rubber vacuum line from the distributor to the
>carburetor without the chamber? ....
I'd say keep the fuel separator. The vac line on the MGA with H4
carbs is connected to a port in the bottom side of the rear
carburetor venturi, just at the bottom edge of the butterfly throttle
plate. This is down stream but quite near to the main fuel jet. If
(when) conditions allow liquid fuel from the jet to dribble along the
bottom of the carb throat, the fuel can enter the vac port and be
drawn into the vac tube en-route to the vac diaphragm on the
distributor. The fuel separator is there to prevent liquid fuel from
getting to rubber diaphragm.
Later model MGB have the venturi vac port on top of the carb throat
where liquid fuel is less likely to enter the vacuum tube. Still
later models use a vacuum signal ported from the top of the intake
manifold where it is extremely unlikely to ever see liquid
fuel. With the bottom venturi tap on the MGA it is more important to
use the fuel separator in the vacuum line to the dizzy.
Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com
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