<VV> Fuel Prices Per Octane-------Now Fuel Pumps

[Frank DuVal]

The test I perform to see if the car has vapor lock, due to high fuel 
pump temperature, is to pour ice or ice water on the fuel pump. If fuel 
then starts pumping to the carbs and the car starts, there you have it, 
hot fuel pump boiled the gasoline inside to a vapor state. Not enough 
vapor can be pumped by the pump to run a Corvair engine and the vapor 
escapes from the carb vent before it gets through the main jet.

Yes, a leaking pump valve can also cause the same symptoms, but usually 
at lower temperatures, and not the same heat soak period of time.

Pressure? As long as I have flow, the pressure could be very low and the 
engine still runs, therefore no vapor lock. Low fuel pressure would be 
more of a high speed problem. If I have vapor, the pressure will be 
zero. Why? because the carb bowl is empty, the needle is open. Therefore 
no pressure can build up in the feed line to the carbs. No, I have never 
taken the pump off and done bench testing to see what the maximum 
pressure would be. That's a good idea though.

All three of my daily driver Corvairs have mechanical fuel pumps. Most 
of the club members around here run mechanical pumps, including one 
daily driver. The one, and only one, that experienced vapor lock is my 
66 AC car, where the condenser heats all the air in the engine 
compartment (not just the engine cooling air like earlier models). I 
tired of carrying ice with me on 95 degree days, so I installed an 
electric fuel pump up at the fuel tank with a switch on the dash. I can 
run it when I need to. I have only needed it once since installing it.

All vapor lock I have ever experienced is of the heat soak type, after 
sitting 10 to 20 minutes with the engine off. Engine starts fine, but 
stops after the carb bowls empty, typically just out of the parking lot. 
I have never had vapor lock while driving or very short term stopping.

Back in the early 80s I started seeing a lot of vapor lock problems. 
Those problem cars got electric fuel pumps. Of course there were lots of 
Corvairs being driven everyday back them. Now I rarely hear of actual 
vapor lock problems. Lots of things thought to be vapor lock, but 
without the heat soak period to boil fuel to vapor. These are usually 
fuel hose, filters, loose pump valves, etc. One should replace all the 
rubber hoses and filters before condemning the mechanical pump and 
switching to electric.

On a side note, I just replaced the electric fuel pump on my Graham. 
Yes, they do fail also.

The throwing of an electric pump to solve a fuel problem is like 
installing a Pertronix to solve a points problem. Sure, it can solve a 
particular problem, just not ALL the problems.

Frank DuVal


On 7/27/2013 12:30 AM, Smitty wrote:
> Smitty Says;  This like certain other subjects has a tendency to feed the
> never ending conflict about Mechanical VS Electric fuel pumps.  Everyone is
> welcome to their own opinion about which is superior.  That's not what I am
> writing about.  Nor am I denying the thousands of poorly manufactured pumps
> made of inferior materials.  I admit leaks are bad.  They smell bad , they
> are a hazard, but they are wet and easy to recognize.  So we won't talk
> about superiority and we won't deny that some mechanical pumps had a
> problem.
>
> What I would like to do is remove a long term burr from under my saddle and
> say, alcohol content in gasoline has not been proven to be the cause of
> vapor lock symptoms in Corvairs.  There will be plenty of people jump up
> here and say they have experienced it, and to them I say prove it.  Before I
> will lower myself to argue the point with anybody I want to know what tests
> you performed?  What was the fuel pressure.  How many strokes did the pump
> take to bring the pressure up to maximum?  How long would the pump hold
> pressure once it was loaded?  Are you aware that a leaking valve in a pump
> can exhibit classic vapor lock symptoms?  Same for stopped up fuel filters,
> either in-line or in the carbs.
> Before you bad mouth the poor old picked on Mechanical pump and re-fire the
> electric pump wars, I suggest you look around a the couple hundred other
> Corvairs around you that are burning the same fuel you are and ask the
> owners how they avoid vapor lock.
>