[T3] Fuel Primer Switch.....

[William Jahn]

My only experience with the having to prime to get my 73 to start was sudden . By sudden I never had an issue until about a year ago , It started right off since I bought it in 85 then I noticed one day on the first try it wouldn’t start and took three key cycles which soon became six . I tried a test by connecting a pressure gauge , built up the pressure then clamped off the line pressure side of pump and it held longer than without the clamp just to test the pumps check valve . I replaced the pump with a modern type with  just an in and out in fear that the old pump might quit because of the check valve then used a small toggle I already had installed in the left  side of the columns lower plastic cover which is just a upper and lower cover you can remove to get a the ign switch wiring. 

 At the time the gas was the same tank and type of fuel . I don’t know yet feel it may be a failure of the pressure regulator not sealing proper once the actual flow stops yet I never replaced the regulator and also it’s possible since the fuel lines from the tank to the engine are still from 2009 and are R7 rated perhaps fuel vapors are released out yet that does not seem likely to cause a sudden change since they do not leak at the connections and I don’t smell it.

 At this point I feel it’s the regulator which can fail by not sealing the return side. It never mattered how hot it got or if it sat for a week it always started first key turn. Now if it sits overnight I can hear air entering the tank using the primer switch. If it sits longer the air into tank sound is longer. 

Sent from Mail for Windows 10

From: Jim Adney
Sent: Tuesday, September 25, 2018 6:39 AM
To: type3 at vwtype3.org
Subject: Re: [T3] Fuel Primer Switch.....

On 25 Sep 2018 at 5:33, J. Jonik wrote:

> Why doesn't turning on the key multiple times, not to point of ignition, prime
> the fuel system?

Turning the key multiple times clearly works, but it adds wear to the 
ignition switch. That's not as much of a problem on your '73 as it 
would be on a '71, where a replacement switch is almost impossible to 
find, but even replacing a '73 switch is much more work and more 
expensive than a primer switch.

I think it's also likely that having a switch that allows you to run 
the pump continuously, as opposed to a series of 1 second pulses, is 
more effective in clearing the air out of the fuel system.

> Then, what's wrong that it NEEDS special priming tricks, or primer
> switches?Is there an old, worn out, or dirty Primer Switch somewhere that ought
> be replaced, or cleaned?

That's the $64k question. I don't know. I've worried about that for 
decades and tried replacing everything in the system without 
discovering the key.

The ONLY remaining suspect I have is the fact that when these systems 
were new, all the fuel lines in the engine compartment had grey vinyl 
covers over the gas lines. It's possible that this gave just enough 
extra heat shielding that the heating/boiling problem didn't occur.  

Over time, as we replaced those hoses, those sheaths were discarded, 
because they were too hard to get over the new lines. Plus, most of 
the time the new lines were larger than the OE so it would have been 
impossible to slide the sheaths on.

It's also possible that this problem always occurred in our hotter 
climates, and that it has gotten worse with global warming (yes, it's 
real) and possible changes in the vapor pressure of modern gasolines.

I designed the primer switch kits to solve this very common problem 
simply and cheaply. They're effective and cheap. They work.

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

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