Rapid pumping does indicate empty float bowls. If you have the Hall-effect
pump, rather than the transistor assisted points type, I don't trust them.
My V8 has one and started doing what you describe, in my case it was weak
pumping, it was only taking itty-bitty strokes i.e. not enough throughput.
I took the pipe off the carbs and fed it into a bottle while I watch the
action of the pump. Couldn't see anything apparently wrong, and after a few
minutes it just started pumping normally again. My pump is not a conversion
so I cannot convert it back to points again at the roadside. I now carry a
spare pump.
I've never really understood 'vapour lock' in connection with our fuel
systems. If the fuel level in the float bowls drop the valve opens. With
the pump at the back of the car pushing, even if there was vapour in the
pipes wouldn't it get pushed straight through to be followed by liquid fuel?
Or is the theory that the pipe gets so hot that the liquid fuel also
vapourises at that point? But that takes energy that would tend to reduce
the temperature of the pipe, unless there was so much heat being generated
in the engine compartment that there was more than enough to keep the
vapourisation going. That's an awful lot of vapour. My factory V8 has
never suffered from vapour lock even on a 90+ day stuck in traffic, with
both fans on full time and the temp needle well into the red.
PaulH.
http://freespace.virgin.net/paul.hunt1/
(or if that URL doesn't work try )
(http://194.168.54.52/paul.hunt1)
-----Original Message-----
From: James Howard <jhoward@sextans.lowell.edu>
To: MG list <mgs@autox.team.net>
Date: 19 November 1999 04:32
Subject: Stumbling
>
>I had a problem the other day with my 66 MGB/GT that I can't figure out.
>It has been convereted to negative ground, and has a newish SU fuel pump
>that has electronics controlling it rather than points.
>
>We live in Flagstaff, AZ, elevation 7000 ft. The nights are getting into
>the 20's F, and I suspect that the gas we are using this time of year is
>the winter formulation.
>
>We drove down to Sedona, which is at 5000 ft, and you drive a beautiful
>two lane road through Oak Creek Canyon to get there. It was 95F when we
>got there. On the way down, after driving for about 45 minutes, the car
>started stumbling a little. I stopped to make sure the connections in the
>ignition circuit were tight (they were), and continued on. On the way
>back up, the stumbling returned, and finally the car quit. After opening
>the hood, scratching my head, looking for anything obviously wrong for a
>few minutes, I started it up again. When I turned the key to run, the
>fuel pump went crazy for a few seconds, like it does when the float bowls
>are empty after rebuilding the carbs. So, we drove up the road, when it
>started stumbling again. I was thinking vapor lock, so we stopped for
>lunch for an hour. After that hour, we had no further problems on the way
>back to Flagstaff.
>
>I am thinking this was vapor lock. My Dad, who owned a then new 67 BGT in
>Colorado, says he never had a vapor lock problem with it. So, he thinks
>it is the fuel pump. I think that gasoline is a lot different now than it
>was in 1967, and the winter gas in hot weather could cause this problem.
>
>I was wondering, what do you all think?
>
>Thanks,
>
>James Howard
>
>
>
>
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