[Zmagnette] H2 leakng at float bowl junction

Fletcher Millmore gofanu at cust.usachoice.net
Sun Apr 6 13:43:38 MDT 2014

My info is direct from the Master SU parts catalog.
Without going through hundreds of variants, it appears the ZA H2 all 
came with version one, the 3-stepped bolt and fibre/brass washers.
Both versions using grommets appear on MGA H4 and other H4; haven't 
looked if they are also on other (later than ZA) H2.
It would appear that there should be a slight float level adjustment 
between the three arrangements, as the fixings cause the bowls to be at 
a different height. I once figured this out, but it has dribbled away!

But, these things get changed...

and assembled with all sorts of miscellaneous bits added or missing or 
confused - or all of these.

I've never had any trouble with any of these when assembled correctly. 
Biggest issue is likely the lubrication of the bolt threads and 
underhead to get the fibre washers working.

It would seem that grommets would help with vibration in the fuel 
level/float valves, which can be a serious problem with some engines 
under some conditions, probably much more of an issue on highly (or 
poorly) tuned units. I've always thought that is why they changed it, 
and the grommet/bolt system has less parts for people to drop down the 
various holes.

Fast idle in the center hole is a good start, but it is not hard to 
figure out if it might be better. Trouble is, you have to care and you 
have to work fast, before the engine warms up even a little. On an 
engine you live with and drive in winter, it becomes clear if you need 
more or less fast idle to keep it happy. The now usual summer faery cars 
hardly matter.

I used to change mixture adjustments by ambient temperature, and would 
set customer cars for expected average conditions - setting in the 70F 
shop in winter is not good, nor is setting on a 50F night when you are 
going on a hot day cruise. I always offered customers free readjusts as 
the seasons changed too. This is more important than the fast idle 
issue, but it is related in that you need fast idle  effective BEFORE 
enrichment. You can get by with carbs set cold on the odd hot day IF you 
can set the idle speed up with the first movement of the choke knob. 
This also helps a lot on the commonly encountered hot running trouble, 
which has much to do with the observed fact that most people seem to set 
mixture too rich to begin with. And, lots of fast idle before enrichment 
is great for getting your windscreen defrosted and jump starting other 
folks cars!

note correction: dished washer for the bolt/grommet setup is AUC1837 not 


On 4/6/2014 2:09 PM, Steven Trovato wrote:
> Fletcher,
> I will defer to your knowledge on the subject.  Truth is, the carbs on 
> my bench right now that will receive the viton seals in my photograph 
> are from an MGA, not a Magnette.  My statement about the two versions, 
> bolt or stud, was pretty much a quote from the SU Carburettors 
> Overhaul, Tuning and Maintenance video that came from Moss many years 
> ago.  That there are actually more versions is easy to believe!
> I also believe that the different versions are interchangeable as 
> sets.  To repeat Roger's question, do you have a preference for a 
> particular style for reliability and leak prevention?
> While we are talking about these carbs, what is your feeling on the 
> three hole positions in the fast idle cam?  So far,  "just put it in 
> the middle position" is the advice I hear the most.  Do you agree?
> -Steve T.
> At 08:58 PM 4/5/2014, Fletcher Millmore wrote:
>> There are (at least) 3 versions.
>> ZA H2 should have
>> bolt AUC 1541  (two stepped bolt)
>> w/ 2x fibre washers AUC5026  and brass washer AUC5027 underhead (F-B-F)
>>  and thin fibre AUC2130 between bowl and body
>> Later carbs used  a different bolt arrangement:
>> Bolt AUC1835 (single step fat bolt)
>> w dished steel washer AUC1887 underhead
>> 2x AUC 1584 rubber grommet
>> Later stud arrangement is:
>> Stud ("banjo pillar") AUC1887
>> fibre AUC1884 (I think fibre, may be copper, not specified except as 
>> "plain") underhead to body
>> Flat steel washer AUC1889 against pillar hex
>> AUC1584 grommet x2
>> Flat steel washer AUC1888
>> Nut AJD8206Z
>> I believe all of these are interchangeable AS  SETS - but it is V 
>> common that they are mismatched and incomplete.
>> As I always recommend, lubricate the threads and bolt underhead with 
>> Lubriplate, and soak the fibre washers in warm oil for a few hours to 
>> eliminate leakage problems.
>> FRM
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