To the person getting a stumble letting off the gas, pushing in the clutch,
and hitting the brakes. When the mixture was adjusted to give the highest
vacuum at idle, you did optimize for that particular moment in time.
However, carbs are relatively simple devices that can only compensate so
much for changes. When you step on the clutch, you increase the load and
slow the engine down. When you step on the brakes, the engine sucks in a
big bolus of air from the brake booster to create the vacuum boost. The
added air weakens the mixture at the same time the extra drag asks for more
fuel and the fire goes out. That is why most carburetors run richer than
optimum most of the time. They need to cover for the times when the
mixture goes lean and the can't adjust. Give the mixture knob a little
twist and life will be good. This is especially true in the winter when
more fuel is liquid and everything is colder/ harder to
turn/light/evaporate.
A cracked head can run fine but it depends where it is cracked. For
instance if the crack is between the valve seats you could replace the
exhaust seat and live with a slight leak on the intake. The exhaust would
burn out if you left the crack there. On the other hand, good used heads
are available so why bother? As far as needing new seats for unleaded
fuel, it depends. If you clean the exhaust seat and valve to bare metal,
you will most likely see valve recession. On the other hand if there is a
good build up of lead deposits on the valve and seat, it will last a long
time. I adjust the exhaust valves on the MGA after about 200 miles of
freeway driving after putting in new (stellite because that is what was
available) valve and hand grinding the seats clean. If money is tight,
just do the exhausts. This will also reduce the chance that the hardened
seats will fall out. Years ago I had a head shop (not that kind) refuse to
put in both intake and exhaust hardened seats on an MGB because they would
touch each other and be much more likely to fall out. The exhausts are the
only ones that recede quickly so why not take the safe compromise approach
and just do hardened exhaust seats. That is what I will probably do this
spring.
On fuel pump orientation. As long as the fuel is delivered, I would think
that what the pump does under there is its own business.
Regards,
Bill Eastman
61 MGA
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