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

[Bob Spidell]

Hi Rich,

Are you saying the 'book' setting is too tight, or that the pumps aren't set 
according to the book (something like 'screw the diaphragm in until the points 
don't throw over, then back off 2/3 turns')?

The arcing occurs when the points open; if the coil is saturated with a 'normal' 
setting, having the diaphragm too tight won't matter (the coil might overheat, 
though).  Once saturated the coil won't draw any additional marginal current due 
to the induced impedance in the coil.


Bob


Rich C wrote:
> 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

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Bob Spidell           San Jose, CA            bspidell at comcast.net

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