[T3] New FI Primer Switch

[Jim Adney]

I have a new design FI fuel pump primer switch kit that I've been 
testing for a few months. I don't really have much experience with it 
yet, but I did get a few tries in last fall, before my '73 Square got 
snowed in.

It was warm here in Madison today, so I started both my '71 and my 
'73. I'd been intermittently charging both batteries over the winter 
to try to keep the batteries alive, so both started easily. The '71 
has the old, original pushbutton primer switch, which has the 
advantage of being cheap and does the job that is most often needed: 
clearing air out of the fuel line before running the starter.  

The newer system on my '73 uses a heavy duty toggle switch that has 3 
positions: OFF/NORMAL/(PRIME) PRIME is momentary, spring loaded, so 
you can leave in that position accidentally.

My '73 seems to have a problem with 1 or 2 injectors that leak and 
inject too much gas when I first start. That floods those cylinders 
so I end up trying to drive on 2 cylinders with poor gas mileage, no 
power, and severe ring/cylinder wear. The 3 position switch allows me 
to turn the pump off while the engine is running, which flushes the 
excess gas out of those cylinders as the pressure in the line 
decreases slowly and the other cylinders continue to run, but lean. 
It takes a bit of fiddling, but it works. I can turn it off and hear 
the engine run on 2-3 cylinders for awhile, then start to slow down 
as those cylinders lean out, then speed up as the other cylinder 
catches and fires. If I turn the switch back on just before the 
engine dies, I'll get all 4 cylinders.  

I can also turn the switch OFF before I turn the key OFF and allow 
the line pressure to bleed down, which minimizes the amount of gas 
that might leak into the leaky cylinder if the engine was shut down 
with full pressure in the line.  

As a bonus, if you leave the key off when you park the car, no thief 
will know to turn it on to steal the car.

Later today, I had to run an errand, so I took the Square and got the 
engine warmed up. When I got home, I shut off the switch and timed 
the engine to see how long it would run after the fuel pump stopped. 
This was at idle with the engine somewhat warm. I was surprised that 
it ran for over a minute.

At about 60 seconds it started to stumble a bit, but it seemed like 
the FI was responding by trying to add more fuel, which kept it going 
for another 15 seconds. Wow, 75 seconds total; this was more than I 
expected. I was surprised.

I don't have a batch of those kits ready yet, but let me know if 
you're interested and I'll make up a few. I think I can sell these 
kits for ~$25 The kits will come with complete instructions, mounting 
bracket for under the dash, and all necessary wires already soldered 
to the switch. Installation requires no soldering, just unplug and 
plug wires, and bolt the switch in place.

The earlier, cheaper primer kit will remain available for $10/$11 
(MT/AT.)

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