Interesting. Have owned my MK I (not MKIA) for a long long time and
never had a vapor lock. Had the pump quit a time or two and prompt
whapping it with a small hammer like object would start it going again
until I could get to a replacement part. Vapor lock occurs between the
pump and tank. In the old mechanical pump system it was fairly common
because the pump was generally higher than the tank outlet and the pump
had to lift the fuel with a small vacuum. This slightly lowed fuel feed
pressure and hot gasoline would cause the fuel to tun to vapor. The pump
would not pump the vapor and so the float bowls run dry. Had to wait
until the fuel cooled enough to return to a liquid and then a small
amount of cranking usually filled the bowl and the car started. Most
electric pumps are put close to the tank and the fuel has no heat
source in that area to heat it up. And the fuel has only a short
distance to the pump so the pump is easily supplied. The Facet pump is
a continous duty type as I recall (I now have one on my car) and it runs
all the time. Not sure how that would affect the pump feed though. If
the pump is getting fuel, t will pump fuel forward. So, perhaps you
have another issue? Like perhaps the line to pump is undersized, or
slightly plugged. It would be interesting to see the fuel line temps
when it is running and not pumping. Do you have a laser temp reader? Do
that in a few places and see what is going on?
mayf
______________________________
drmayf
Worlds Fastest Sunbeam, period.
204.913 mph flying mile
210.779 mph exit speed
On 6/2/2011 6:38 PM, Stu Brennan wrote:
> It was a hot day, no breeze, I just got home in the Tiger, and let it
> idle in the yard a couple minutes while I got something out of the
> garage. I was also interested is seeing if my new horn block off plates
> made a difference with the temperature rise (maybe a bit). But before
> the temp got too high, I heard the fuel pump (a Facet type) start
> clattering away, a sure sign of vapor lock.
>
> So, being an engineer, I wondered what could be done about this.
> Relocating the pump to the spare tire well (its now in the stock 1A
> location) might help.
>
> But what could I use to cool it in its stock location? Suddenly I
> thought of an answer. Fuel!
>
> At idle the fuel flow is extremely slow, giving it plenty of time to
> heat up in the pump and the lines. But if it was flowing faster... Has
> anyone ever considered putting a "T" in the fuel line up near the engine
> and adding a solenoid valve and a return line to the tanks? Then if
> vapor lock was detected or expected, the fuel flow could be increased
> with no loss, continually cooling the pump and lines with much cooler
> fuel from the tanks.
>
> Crazy idea? Any other thoughts?
>
> Stu
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