Vapor Lock

The last few years, I had noticed that the car would start to vapor lock on hot days.  Usually, quick application of the electric fuel pump would keep the car from stalling and I could continue the journey.

I looked into this, doing some measurements, trying to figure out if the phenolic block needed to be thinned down.

Since the fuel tank was full, I didn't disconnect the fuel lines from the mechanical fuel pump, but simply pushed it up and back to be out of the way from the block and push rod.  First I measured the stroke on the push rod coming from the block.  It ranged from a minimum of .410 to .504", for a stroke of .094".  There was a single gasket on the pump side of the phenolic block that was .017" thick.  I tried to measure the stroke of the lever in the fuel pump, but with it still attached to the fuel hoses, it was difficult to get an accurate measurement.  But in the end, I decided that simply removing the gasket would not cause the pump to be over-stroked, I put everything back together sans gasket.

I did measure the stroke of the same model FISPA 150 pump from the PF coupe.  The maximum stroke (at the lever where the push rod goes) was .066".  It is difficult to measure as it takes a lot of pressure on the lever to move the diaphragm and spring to the maximum stroke.  I found it easier to remove the plate on the pump.  That exposes the levers at the bottom of the diaphragm shaft so one can use a screwdriver to actuate it.  Then with something to hold the screwdriver in place, more accurate measurements can be made.  One thing of interest is that the stroke of the pump rod on the 330 is more than the stroke possible on the 250 pump.  So if that pump were used with no free play at the end of the rod, the lever/diaphragm couldn't move enough to accommodate the the rod stroke and something would break.  I have heard of cases where the lever will break if that happens.  Now it is possible that the diaphragm in the 250 pump is so old and stiff that it does not move as it should.  If I have need to take the 330 pump again, I will measure the stroke on it.

I was hoping that the gasket removal would solve the vapor lock issue, however, a recent trip to the Forest Grove Concours proved that not to be the case.

After getting back, I fixed up some fittings so I could attach a fuel pressure gauge to test the pressure from the electric fuel pump, pressure regulator and the mechanical fuel pump.

For the fuel log end, I used a piece of clear tubing with a 1/2" ID.  That clamped onto the threads of the log and with short piece of 1/2" rod clamped on the other end, allowed the engine to run only on the electric pump  by blocking off the front of the fuel log.

    

To measure the mechanical pump and pressure regulator pressure, I clamped a piece of that tubing onto a spare banjo fitting (courtesy of Lowell Brown).  I had to put a smaller piece of fuel hose I had around that screwed tightly onto the banjo fitting.  Then the plastic hose slid over the rubber section and a clamp held every thing securely with no leaks.

   

Well, the mechanical pump after the regulator was putting out a steady 5½ psi.  That's exactly what it should be.  I didn't bother to measure the actual pressure at the pump since it was OK after the regulator.

With a piece of tubing running to the gauge from the front of the fuel log, I was able to measure electric pump pressure with the engine not running.

The electric pump would put out 4 psi on the stroke, then the bleed line back to the tank would reduce the pressure to 3 psi and the pump would actuate again.

Now I'm back to square one on the vapor lock.  Tom Yang mentioned that he's been seeing more occurrences of vapor lock and he thinks that it is due to a higher concentration of ethanol alcohol in the fuel during the summer months.  The ethanol which has a lower boiling point is causing the problem. On his 330 America, he added a second electric pump to increase the volume of fuel.  I will consider this.  A nice quiet one mounted at the rear by the tank could run all the time and never be noticed.  Of course, modern cars with fuel injection have pumps that run at 40 PSI or more, so fuel with a low boiling point is not an issue.

My friend Buddy Obara mentioned that he had a problem that sounded like vapor lock to me.  His problem turned out to be an old cartridge in the fuel filter by the tank.  So I ordered a couple of filters since I can't remember how long it's been since I changed it.  At the same time, I decided to restore the can the filter sits in.  Mine is painted black with no sign of the yellow FISPA decal that is supposed to be on it.  Here's a picture of one on Lowell Brown's car taken many years ago next to mine.

   

It did have a layer of dirt or sand in the bottom, but no rust.  I also found a plate on top of the filter housing that I didn't know was there.  Not surprising given how much dirt was on top.

       

I stopped by a model shop and got a can of Tamiya paint in TS-91, dark green as it looked closest to the color on Lowell's can.  Parker Hall has the proper decals, but when I called him, there was no answer, so I spent a couple of hours doing the artwork to print my own water transfer decal.

After some bead blasting, primer and the Tamiya paint, here's what the can looks like now.  The decal didn't turn out as well as I wanted.  I will probable end up using Parker's.  At least the green color came out pretty close.

I also added a second electric fuel pump.  This one is the same as one for a 308 carb cars, a Facet 6 PSI model.  Tom Yang had some special banjo bolts made up to easily add a second pump.  They are a standard banjo bolts with a nipple coming out the head of the bolt.  So one just replaces the regular banjo bolt and adds some 3/8" fuel hose going to the new pump, inlet to inlet, etc.  That makes the new pump work in parallel, providing a lot more fuel flow.  The power is drawn from the same wiring, so both pumps work when you turn on the A switch.

    

I built a bracket that attached to the existing pump's bracket so the new pump ended up mounting on the other side.

At the same time, I added a heat shield above the exhaust pipes which run right under the filter and pumps.  Hopefully, all of this will prevent any vapor lock in the future.  I started with some aluminum and rolled in a couple of beads for stiffening.  This was to match an original heat shield that covers the forward cans.

   

Then I formed the rounded edges by hammering it over a pipe.  Next I made some brackets designed to clamp to the exhaust pipes and hold the head shield away from the muffler.

   

The brackets were pop-riveted to the shield and clamped to an exhaust pipe at each end.  I think I'll swap out the stainless steel screw clamps for regular muffler clamps the next time I go to an auto parts store.  You can see how the FISPA pump is just a couple of inches directly above muffler.  The fuel filter is in the same area next to the pump.

Hopefully all of these changes will preclude having a vapor lock issue in the future.  Here's everything buttoned up.