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.

Add the under car air spoilers to help disturb the air in the engine compartment. You can find old ones or craft up some made of aluminum.

Previous link:
http://www.914world.com/bbs2/index.php?showtopic=119895

It seems that the problem is finding a way to exhaust the very hot air that is under the car, which the early, full valence does a nice job of trapping. I have seen some very nice rear valences that have been louvered or have had some neat cooling slots cut into them, but of course that wouldn't pass as OEM. When the car is sitting in 90 degree, stop-and-go traffic, and there is no airflow passing beneath the car, and the fuel is percolating in the lines by the fuel pump, it seems that either the fuel pump gets moved, the rear valence comes off, or I live with a constantly stalling car in hot weather traffic.

Can you install a fuel pump under the tank as the factory later did, and then run a dummy fuel pump the stock location so it looks right, but works?

I've seen people run trickier setups to skirt rules or just cheat

It's not as dirty a trick as plumbing your nitrous under your manifold on a V8.

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

I think there's an easier fix here if you want to stay OEM and have an early four.

Run the snowplow in cooler weather, and replace it with the later version in hot weather. The replacement version (short) is a factory authorized replacement, since the "plow" was deleted. Seriously doubt that many judges would fault the replacement, except at a Parade concours. Most contemporary judges would allow the short version, much like the replacement battery cover.

It's quick & easy to change them.
Pat

Try me. I'll nick you faster than it takes to get your car on the road. <grin>

My '70 914-4 rarely vapor locked (more promblems with stcking starter solenoid). Only time I had problems were after DE/time trial runs. My solution (dumb luck perhaps) was to wire the fuel pump with a switch power source to keep it running after a hard/hot drive. I've long since removed the wiring and have never had a problem since. Then again I don't do track events anymore.

Interesting. So how would you deal with fact that the short valance was an authorized factory replacement? Similar, but not the same as the cobbled up Audi battery cover as an authorized/mandatory replacement for the splat cover & modified bungee cord early model batter cover.
I'd have tp take issue with this.

Audis of the era didn't have a battery cover, other than the back seat cushion ....................

The Cap'n

I look at it no different than a '70 with Fuchs on it. They were not available for that MY. We are talking Concours events, yes? The Audi battery cover would be acceptable as it WAS a mandated replacement stateside (DOT). I don't think it was such overseas, though I could be wrong.

True, but when Audi moved the battery to the front they did have a hard plastic cover. Had one. In the era of non-sealed batteries, its purpose was stupid. Battery acid continued to build underneath and went down with rain, so its purpose was stupid. Though mandated.

I pitched the Audi cover years ago & still use the rubber band held plastic piece. After 40 years I still have no hell hole issues, though my battery tray needs repainting.

Remember, the battery cover recall was made at least 5 years into 914 production cycle. Audis had changed.