[alfa] Backfire mystery

[Scott Johnson <scott@xxxxxxxx>]

For nearly a decade I've been putting up with a backfiring spider. Why? 
1971 spider with original SPICA... say it with me folks, "bad 
microswitch and/or fuel cutoff solenoid". The latter is easy to fix but 
expensive, the former a b*tch to fix but cheap. I just put it in neutral 
when decelerating.

Well, while doing a final SPICA adjustment yesterday, I noted the test 
procedures for the fuel cutoff system. Got nothing else to lose, so I 
thought, "why not?" First tested the cutoff solenoid, which shut the 
motor down nicely when activated with a wire to the battery. Then got 
out a test light and followed the procedure for the microswitch. Stuck 
the probe into the spade, bumped the motor up to 3000, then let the 
throttle snap shut. Imagine my surprise at being greeted with a bright, 
strong light that went out precisely at 1600 rpm just like it was 
supposed to! Put it all back together for a test drive and sure enough, 
no more backfiring.

I can only think of two things: either the spica pump was so wildly out 
of adjustment the microswitch just didn't kick in properly, or there's a 
short somewhere. Strongly suspecting the latter now... maybe I'll just 
put a new connector on.

Oh, and on a related note... anyone know exactly how the cutoff system 
works? Does it put the pump section into neutral somehow, or does it 
simply shut off the flow of gas? If the latter, that would seem to put a 
dent in the "never ever run it out of gas because you'll ruin the pump" 
school of thought.

Any rate, felt like sharing. Thanks!

Scott J.
71 1750 Spider
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