[Healeys] SU Pumps Bad Rap (was No Power)

Rich C richchrysler at quickclic.net
Sun May 31 07:12:34 MDT 2009


I'd like to share an observation here:

Last year we prepared a 1954 BN1 with an amazing 4126 original miles for the 
road after the car had been stored for over 4 decades. The entire fuel 
system was filthy and had to be thoroughly cleaned. New kits went into the 
carbs, the tank was removed, cleaned and sealed, the lines were blown out, 
etc.

The original single point SU pump was cleaned thoroughly, the points were 
cleaned and the setting checked. Initially the pump struggled a bit with the 
stiff diaphragm, so I "exercised" the diaphragm gently by inserting a small 
flat blade screwdriver under the rocker pedestal and levering the stem up 
and down a few times. Then current was applied and away it went with a 
steady strong beat. Everything was reinstalled and the car has been running 
flawlessly for the last year and a half.

As for many SU pumps installed either new or rebuilt, I believe a lot of the 
arcing problem and so called unreliability can be traced to the diaphragm 
not being set correctly, causing undue arcing as the diaphragm struggles to 
complete it's proper "throw over". I see this on almost half the new SU 
pumps. In those cases, a 1/3 turn (2 screw holes) of the diaphragm setting 
to allow a slightly longer stroke does the trick.

As an aside, the above mentioned BN1 (original and extremely rare one of 7 
done in Gunmetal Gray Metallic with red trim) will be one of four survivor 
cars being reviewed at an indoor tech session at Conclave in Kingston, 
Ontario 3 weeks from now. Hope you are planning to be there.

Rich Chrysler


Bob Wrote <snip>
> re:
> "I think SU pumps have a bad wrap"
>
> Not necessarily.  IMO, the problem with SU pumps is they use points to 
> switch the current.  When the points open the induced magnetic field in 
> the coil collapses producing a back current which arcs across the points 
> (similar to what happens in an ignition coil).  This arcing transfers 
> metal with each occurrence, and also produces ozone which exacerbates the 
> arcing (that's why the electronic end of the pump is vented).  Eventually, 
> the gap changes and/or the points stick and the pump becomes intermittent 
> or fails outright.  The arcing is why SU pumps went from nothing, to a 
> capacitor to a diode (called a 'flywheel diode') across the points to 
> reduce the arcing.  The final cure is a fully electronic pump, with a Hall 
> Effect and transistor-switched design (which solved my pump problems--I've 
> never had a contamination problem).
>
> Also, the diaphragm can get stiff from age and non-use.

Alan Wrote <snip>
>> To be honest as I get older I think SU pumps have a bad wrap. They
>> actually work fine, but they fail usually when they get clogged with
>> crap.
>>
>> All cars I buy, I ALWAYS pull the tank and fuel pump and clean them
>> out thoroughly.


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