MGALUVR@aol.com wrote:
>
> Hello to the list,
>
> I recently had a rebuilt early MGB 1800cc, 3 main bearing engine installed
> in my 62 MKII MGA roadster. Everything has gone well and the car runs nicely,
> with the exception of one thing that needs attention. I have some gas that
> drips from the bottom of both carburetors after I shut the car off and park
> it in the garage. The smell of gas is distinct and the odor lingers for an
> hour or so after shutoff. I assume the pressure built up by the fuel pump in
> the line causes the slow but steady drip until the pressure is gone. There is
> only a small amount of gas that is involved. And because the amount is small
> it probably evaporates almost as quickly as it leaks. I put a pair of SU's on
> this engine that were left over from the previous engine (1622 CC). I assume
> these that are currently in use are the 1 1/2 inch variety. I know there are
> also 1 3/4 inch SU's out there also. Were these larger carbs standard on the
> larger 1800 cc "B" engine ? I have the carbs that came on the rebuilt motor
> but they are not rebuilt and since they were questionable, I went with what
> came off the previous motor. I didn't know their condition either, but they
> physically looked to be in better shape. Would a pair of 1 3/4 inch SU's give
> me any appreciable performance boost? If the carbs that came on the rebuilt
> motor are actually the larger models I will have them rebuilt instead of the
> ones I am using now. What cars were the larger SU's normally used on? Happy
> Holidays, and Merry Xmas to all on the list.
>
> Bill Dillstrom
Bill, I might be able to answer some of your questions, although I
don't own a B. I have a well-loved Victor MG TF 1800, which is
basically a complete MGB powertrain, suspension and brake system,
mounted on a proprietary steel frame designed so that the layout of
the B components mimics the TF geometry, with a fiberglass TF body
and genuine TF chrome, bumpers, cloth top, etc.
I use a special intake manifold and a single 1 3/4" HIF SU carb on
my Cooper S.
It provides adequate carburation for the very modified engine, it's
free from the gravity problem and is easy to adjust. Since there's
only one, the enormous hassle of trying to balance twins is
eliminated.
If I were in your shoes I would try adding the extra breathing
ability you get by adding a set of K&N turbo cone filters and
setting aside the standard air filter setup. Make sure you keep them
clean and oiled properly. The HIF carb has the floatbowl built-in
and centered under the carb body. The old style has the float bowls
to the side of the carb. This introduced the problem that in a Mini,
where the configuration was transverse, one carb would go too rich
and the other would go lean in corners, where gravity could work on
the fuel delivery. In straight ahead configurations like MG's and
Healeys, it would be a similar imbalance, but during acceleration
and braking, braking not being a problem, since no power is required
from the engine, but acceleration was a major problem, because it
could make the back two cylinders go lean at a really good time to
cause maximum damage to valves, seats and pistons. The HIF cured
this. It also incorporates a screw-operated mixture control instead
of the very fiddly jet-centering and adjusting routine. Most of the
ones I've seen are for a single application, but Scott beavis, from
the Mini community, has a pair of HIF's mounted on his car, so I
know the linkage can be worked out.
I found that the more breathing ability I add, long-gap scatter cams
and stage 3 heads, big exhausts and barely legal silencers, BIG
carbs and freeflow filters, the more pronounced the ram effect
becomes. As long as the fuel-air mix is continuing to take that
little step back because of the valve overlap, the engine will
produce normal, stodgy, power. As soon as the speed of the gas mix
column reaches the point where the reversal in direction is
impossible, the engine will take off like a goosed mule, resulting
in that neck-snapping acceleration we love so well. If you use a
standard cam, this isn't a problem and the more it can breathe
freely, the better it will run, as long as the fuel delivery keeps
up with the airflow. This is why I suggest a less restrictive air
filter as a first step.
-Rock http://www.rocky-frisco.com
--
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JJ Cale Live (w/Rocky): http://www.rocky-frisco.com/calelive.htm
The Luggage Fan Club: http://groups.yahoo.com/group/luggage-fans
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