[T3] Why is it that when I got my 73 SB I never had to turn the key several times to prime the system .

[Jim Adney]

On 3 Aug 2017 at 15:12, William J wrote:

> I need to add a switch pretty easy. Yet up until 2011 even if I didn't drive it
> everyday I never had to do this. Now if it sits for one day I need to cycle the
> ign at least 6 to 7 times before it will start . 

It's impossible to be sure, but I don't think the cause of this is 
that the check valve has failed. This was a problem in some of our 
cars even when they were new.

One difference that may be important is that, when new, all the fuel 
hoses in the engine compartment had grey vinyl oversleeves. These 
probably had a small effect as heat shields that kept the hoses from 
getting as hot in the heat soak after shutdown.

The problem you're experiencing is due to the gas boiling after 
shutdown, which forces all the gas back thru the pump, leaving the 
lines filled with vapor rather than fuel. The reason it flows 
backwards is that it takes 30 psi to flow forwards but only 20 psi to 
flow backwards. (The valve in the pump isn't really a true check 
valve; it allows reverse flow above 20 psi.)

An OE solution might be to replace the vinyl sleeves, but I haven't 
found anything I really like for this. My solution is to provide a 
switch to prime the system before trying to start the engine.

You can provide your own switch or I sell complete DIY kits with 
instructions to add them to any FI Type 3. The cheap, $10, kit is 
just a simple pushbutton that you push to run the pump before 
starting. The $30 kit has a heavy duty 3-position (off, normal, 
prime) toggle switch that adds an OFF position that disables the pump 
in case of flooding and provides some extra theft protection.  

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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