on valences and vapor lock, a downside to originality Options

[1970 Neun vierzehn]

For thirty-one years I had run my 70/4 w/o a rear valence panel of any kind (see 3rd photo). After prolonged driving in hot weather or hard driving in warm weather (ie autocross), the car was afflicted with vapor lock (fuel pump in original location).
Keeping the gas tank mostly full helped alleviate the problem.

Now, since the OEM "deep" valence is in place (see 1st and 2nd photos), just a moderate run of 12 miles in warm temps causes vapor lock problems with an almost full tank of fresh gas. We all know that the factory installed a shorter valence later in the 914s' model run. One reason typically cited is the panels' tendency to collect debris and snow(!), but another less emphasized reason was no doubt the increase in engine compartment/rear trunk/under car temperatures.
The shortened rear valence and repositioned fuel pump no doubt greatly reduced the vapor lock problems but early 914/4s are still seriously afflicted if configured as originally built.

[sixerdon]

You know, it's interesting how the vapor lock afflicted the /4's and not the /6's. I had the same issue with a '74 2.0 35 years ago. But all of my /6's as well as others I have spoken with over the years, never had a vapor lock issue. Same fuel pump location and same deep rear valance. Tell me the /4 runs hotter than the /6. Maybe it's the low pressure /6 pump vs the high pressure /4 pump. I used to carry a water spray bottle to spray the pump to cool it down which worked for the short term. Again, this was only hot weather above 80 degrees.
Two years ago I was driving my '75 at a crawl out on the Mass Pike in 1st/2nd gear for 20 miles in 90 degree heat (which was hotter under the car). The fuel pump up under the tank never failed. Since I've owned my current cars, I've never experienced the problem again.

Don