SU float cover warped?

[Shannon Nelson]

I have a '72 MGB with the standard HIF SU carbs. Usually they work
great, but the front one has recently been leaking. I had someone
do an overhaul, assuming they'd replace all the seals and find any
issues, but it is still leaking. Taking a closer look at it myself,
it is definitely the float bowl seal, leaking around the square "O"
ring. The ring looks to be in good condition, and the screws were
tightened down appropriately. I tried a new (round) "O" ring and it
leaked just as much, if not more. In its current condition, screwing
it in doesn't completely close the gap around the ring seal, thus the
leak.

It looks to me like the bowl cover is warped. When I invert it on a
flat surface, the corners touch and the centers of each side are off
the surface. Is this normal, or did someone tighten it down too hard
once and bent the corners in where the screws go?

Do I need to get a bigger O ring or a new float cover?

Thanks,
sln
--
================================================== ====================
Mr. Shannon Nelson Parents can't afford to be squeamish.
sln - at - onemain dot com

[Rob]

Shannon Nelson wrote:

> I have a '72 MGB with the standard HIF SU carbs. Usually they work
> great, but the front one has recently been leaking. I had someone
> do an overhaul, assuming they'd replace all the seals and find any
> issues, but it is still leaking. Taking a closer look at it myself,
> it is definitely the float bowl seal, leaking around the square "O"
> ring. The ring looks to be in good condition, and the screws were
> tightened down appropriately. I tried a new (round) "O" ring and it
> leaked just as much, if not more. In its current condition, screwing
> it in doesn't completely close the gap around the ring seal, thus the
> leak.
>
> It looks to me like the bowl cover is warped. When I invert it on a
> flat surface, the corners touch and the centers of each side are off
> the surface. Is this normal, or did someone tighten it down too hard
> once and bent the corners in where the screws go?
>
> Do I need to get a bigger O ring or a new float cover?
>
> Thanks,
> sln

My guess is that the needle and seat are not shutting off the fuel and
that carby is flooding for starters.

rm

[Richard Porter]

On 1 Aug 2004 Richard Porter <dontusethis@address.uk.invalid> wrote:

> On 1 Aug 2004 Shannon Nelson <sln@onemain.com> wrote:
>
> > I have a '72 MGB with the standard HIF SU carbs. Usually they work
> > great, but the front one has recently been leaking. ...

> I'm not familiar with multiple HIFs. I would have expected HS carbs on
> a '72 B but the 'square' O-ring certainly ties in with the HIF.

Just checked up on this. The HIF4 came in in '72, but the O-ring is
circular even if the float chamber cover is squarish. So where's the
square one? I can't find any reference to it. Have you got the ASU
fitted?

> My suggestion is that you buy a gash carb from an autojumble or a
> breaker and swap the base plate over. Make sure that the plate fits
> snugly over (under?) the body before you tighten the screws!

Also read the bit in Haynes about checking the float level dimension.

--
Richard Porter
Mail to username ricp at domain minijem.plus.com
"You can't have Windows without pains."

[Shannon Nelson]

Richard Porter wrote:
> On 1 Aug 2004 Shannon Nelson <sln@onemain.com> wrote:
>
>>I have a '72 MGB with the standard HIF SU carbs. [...]
>>
>>It looks to me like the bowl cover is warped. [...]
>>
>
> I assume you mean the base plate? It sounds like it's warped, but I

Yes, the "base plate" is probably a better description. That would
curb the confusion about flooding. This is gas leaking from the
bottom of the carb. See part #32 in this Moss Motors picture:
http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28997

Let me better define the "square o-ring". It is a circle that surrounds
the float chamber, but the rubber has a square cross-section rather than
a round dough-nut cross-section. This is item #33 in the same picture.

> My suggestion is that you buy a gash carb from an autojumble or a
> breaker and swap the base plates over. Make sure that the plate fits
> snugly over (under?) the body before you tighten the screws!

Hmm - this is a good idea. I haven't done much junkyarding lately.
I'll have to see if there's still a place out here (Oregon, if you
care) that might have some parts.

> Have you got the ASU fitted?

Nope.

Some update info... A couple of months ago I had a leak in the other
carb, and it was definitely a sunk float. I had a garage do a tune-up
on the carbs, and they found and fixed the float. I suspect it was them
that used the square ring. After I posted my original note yesterday, I
remembered that I had a pair of unused gasket sets hidden away that
would have "new" o-rings. I put them in, and with some careful work
I was able to put the base plates back on with no remaining leakage.
Now I'm back on the road and there's no smelling up the house with gas
fumes.

I was pleased that I could do all this without actually taking the carbs
off the engine: take the air filters off and there's just enough room
to work between the fender and the bottom of the carbs.

I'm still worried about the possible warpage. The Haynes SU manual says
nothing about an odd fit, and I didn't find any comments on the web
about it thru Google.

Thanks,
sln
--
================================================== ====================
Mr. Shannon Nelson Parents can't afford to be squeamish.
sln - at - onemain dot com

[Grimly Curmudgeon]

It was somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Shannon Nelson <sln@onemain.com>
saying something like:

>Let me better define the "square o-ring". It is a circle that surrounds
>the float chamber, but the rubber has a square cross-section rather than
>a round dough-nut cross-section. This is item #33 in the same picture.

It would originally have had a round x-section, but has squashed down
over the years. Replace it anyway.

You could grind the baseplate back to flatness simply by using a piece
of plate glass and grinding paste or fine carborundum paper.
--

Dave
SE6a

[Shannon Nelson]

Grimly Curmudgeon wrote:
> It would originally have had a round x-section, but has squashed down
> over the years. Replace it anyway.

Actually, believe it or not, this was not the case. That had occured to
me, but this piece was not wide enough to fill the channel that it sits
in. I assume that it was (had been?) tall enough to create a seal, but
the horizontal width was definitely less than the width of the channel.
It essentially fell out when I took the plate off.

Thanks,
sln
--
================================================== ====================
Mr. Shannon Nelson Parents can't afford to be squeamish.
sln - at - onemain dot com