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Re: Still stumped

To: Awgertoo@aol.com
Subject: Re: Still stumped
From: John Harper <AH@jharper.demon.co.uk>
Date: Wed, 5 Oct 2005 08:40:20 +0100
Michael

I may not have all the previous correspondence on this thread and seem 
to recall that a similar suggestion has been made. However-

I don't have an answer here but can suggest that there is nothing 
unusual about an SU pump stopping whilst the starter is turning the 
engine. One normally does not hear this because the cranking sounds 
obscure the pump clicks.

The test specification for SU pumps states that pumping should still 
take place, albeit at a reduced flow rate down to about 10.5 volts. It 
is not expected to operate below this.

When cranking, the voltage available at the starter solenoid terminal, 
where the pump power is picked up from, may well be below 10.5 volts. 
The starter might be taking as much as 400 amps. At this current the 
battery voltage could be well down and to add to this there is a 
significant voltage drop in the long battery lead running from the back 
to the front of the car.

However so long as the starter turns the engine fast enough then none of 
this matters. The float chambers should contain more than enough fuel to 
last until the engine starts at which point the pump should restart on 
its own.

Perhaps this is what is happening; the pump is not restarting when full 
voltage is reinstated. This could perhaps be incorrect pump throw-over 
setting.

If it is; and I admit that there could be many other reasons, then we do 
know that the early SU set up instructions set the diaphragm too tight; 
I know to my cost!

Later adjustment instructions solved this problem.

As they say - Just a thought

All the best

>I ran a heavy (#12) wire from the inboard lower fuse block post (the one from
>which the fuel pump circuit is energized)to the hot lead on the fuel pump.
>Same deal--runs fine when the key is turned on but as soon as I push the
>starter the pump stops pumping and only turning the key off, then back on
>re-energizes it, etc. etc.
>
>I'm done for today and hope that someone smarter than me can figure this one
>out.
>
>I'm stumped--Michael Oritt
>

-- 
John Harper




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